Log Message:
Update lang/elixir to 1.6.0.

1. Enhancements

EEx
- [EEx] Allow markers `/` and `|` to be used in a custom EEx engine

Elixir
- [Calendar] Add truncate to `Time`, `DateTime` and `NaiveDateTime` to
  facilitate microsecond precision pruning
- [Code] Add `format_string!/2` and `format_file!/2` for automatic
  code formatting
- [Code] Support column annotations in quoted expressions with
  `columns: true` in `Code.string_to_quoted/2`
- [DynamicSupervisor] Add `DynamicSupervisor` designed to manage
  children that are added and removed dynamically
- [Exception] Make `Exception.blame/3` extensible by adding an
  optional `blame/2` callback to exceptions
- [Exception] Improve the printing of guards on blamed exceptions
- [Enumerable] Add `Enumerable.slice/1` and optimize many `Enum`
  operations with the new protocol. This allows data-structures with
  index-based random access to provide a non-linear implementation
- [Inspect] Show UTF-8 BOM on inspected strings
- [Inspect.Algebra] Add `:strict` and `:flex` breaks - this gives more
  control over the document fitting
- [Inspect.Algebra] Allow a group to inherit the parent group break
- [Inspect.Algebra] Add `force_unfit/1` and `next_break_fits/2` which
  give more control over document fitting
- [Inspect.Algebra] Add `collapse_lines/1` for collapsing multiple
  lines to a maximum value
- [Inspect.Algebra] Allow `nest/2` to be `:reset` or be set to the
  current `:cursor` position
- [Kernel] Prefix variables with V when emitting Erlang code. This
  improves the integration with tools such as Erlang code formatters
  and the GUI debugger
- [Kernel] Warn on the use of `length(x) == 0` in guards
- [Kernel] Warn if `catch` comes before `rescue` in try
- [Kernel] Warn if heredoc is outdented compared to its closing quotes
- [Kernel] Add `defguard/1` and `defguardp/1` to make it easier to
  build guard-safe macros
- [Kernel.ParallelCompiler] Add `compile/2`, `compile_to_path/3` and
  `require/2` which provide detailed information about warnings and
  errors
- [Kernel.SpecialForms] Support the `uniq: true` flag in `for`
  comprehensions
- [Module] Introduce `@deprecated` and `@since` attributes
- [Module] Emit conflicting behaviour warnings if the same behaviour
  is given more than once
- [List] Rearrange equals and inserts for shorter diff scripts in
  `List.myers_difference/2`
- [Record] Allow `:macros` and `:includes` to be given to
  `Record.extract/2`
- [Stream] Add `Stream.intersperse/2`
- [String] Update to Unicode 10
- [String] Allow passing empty string `match` to `String.replace/4`
- [String] Support context and language sensitive operations in
  `String.upcase/2` and `String.downcase/2`. Currently only the
  `:greek` context is supported
- [String] Support `:ascii` conversion in `String.upcase/2` and
  `String.downcase/2`
- [Time] Add `Time.add/3`

ExUnit
- [ExUnit.Assertions] Perform inclusive checks in `assert_in_delta`
- [ExUnit.Callbacks] Add `ExUnit.Callbacks.start_supervised!/2`
- [ExUnit.Case] Generate a random seed per test based on the test
  suite seed

IEx
- [IEx.Autocomplete] Provide contextual autocompletion: `t Enum.` will
  autocomplete types, `b Enum` will autocomplete callbacks
- [IEx.CLI] Provide hints for developers when a bad host name is given
  to `--remsh`
- [IEx.Helpers] Automatically include specs when showing documentation
  for functions/macros
- [IEx.Helpers] Improve formatting of behaviours and typespecs by
  using the formatter
- [IEx.Helpers] Allow pattern matching and guard expressions when on
  `IEx.break!`

Logger
- [Logger] Add `:discard_threshold` to Logger to help with message
  queue overflow

Mix
- [mix app.start] Add `--preload-modules` to `mix app.start`
- [mix archive.build] Allow `mix archive.build` to bundle dot files
  via an option
- [mix compile] Define a behavior for Mix compiler tasks and return
  diagnostics from compiler tasks
- [mix compile] Track struct dependencies between files and recompile
  them only if the struct changes
- [mix deps] Support `:system_env` option when specifying dependencies
- [mix format] Add a `mix format` task that formats the given files
  (or the files specified in a `.formatter.exs` file)
- [mix profile.eprof] Add a new task for time-based profiling with
  eprof
- [mix test] Run all functions in a describe block by giving the
  `file:line` the describe block starts
- [mix test] Report the top N slowest tests with the `--slowest N`
  flag
- [mix test] Report the number of doctests and tests separately
- [mix xref] Support `--include-siblings` in reports for umbrella
  support
- [mix xref] Add `mix xref graph --format stats`
- [mix xref] Add `--only-nodes` and `--label` filters to mix xref
  graph
- [mix xref] Add `mix xref deprecated` that shows the callsite of
  deprecated functions

2. Bug fixes

Elixir
- [CLI] Support path with spaces as argument to elixir.bat
- [Inspect] Properly handle minus signal for non-decimal negative
  integers
- [Integer] Do not raise on non-integer values in `is_odd`/`is_even`
- [Kernel] Solve a precedence issue between `&` and `|`, such as
  `[&Foo.bar/1 | &Baz.bat/2]`
- [Kernel] Do not load dynamic Elixir modules as `:in_memory` as this
  value is not officially supported by the code server. Instead, use
  an empty list, which is the same value used by Erlang.
- [Kernel] Validate variable struct name is atom when used in pattern
  matching
- [Macro] Fix `Macro.to_string/2` for tuple calls, such as `alias
  Foo.{Bar, Baz}`
- [MapSet] Return valid MapSet when unioning a legacy MapSet
- [Regex] Return a leading empty space when splitting on empty
  pattern. This makes the `split` operation consistent with the other
  operations in the `Regex` module
- [Stream] Ensure `Stream.chunk_while/4` does not emit more elements
  than necessary when halted
- [String] Return a leading empty space when splitting on empty
  string. This makes the `split` operation consistent with the other
  operations in the `String` module
- [URI] Preserve empty fragments in `URI.parse/1`

Mix
- [mix app.start] Improve the quality of reports if app fails to boot
- [mix cmd] Allow `mix cmd` to be invoked multiple times without
  marking it as executed
- [mix deps] Ensure optional dependencies in umbrella applications are
  loaded
- [mix deps.update] Ensure transitive new non-Hex dependencies are
  also fetched when a repo is updated
- [mix xref] Take compile dependencies with higher priority than
  runtime ones when building a graph
- [mix xref] Handle external files for xref callers and warnings

3. Soft deprecations (no warnings emitted)

Elixir
- [Inspect.Algebra] `surround/3` and `surround_many/6` are deprecated
  in favor of `container_doc/6`
- [Kernel.ParallelCompiler] `files/2` and `files_to_path/3` are
  deprecated in favor of `compile/2` and `compile_to_path/3`
- [Kernel.ParallelRequire] `files/2` is deprecated in favor of
  `Kernel.ParallelCompiler.require/2`
- [GenServer] Warn if `init/1` is not defined in `GenServer`. This
  brings GenServer closer to the implementation in OTP and aligns all
  behaviours to require the `init/1` callback

ExUnit
- [ExUnit.Formatter] `:case_started` and `:case_finished` events are
  deprecated in favor of `:module_started` and `:module_finished`

4. Deprecations

Elixir
- [Enum] `Enum.partition/2` is deprecated in favor of
  `Enum.split_with/2`
- [Keyword] `Keyword.replace/3` is deprecated in favor of
  `Keyword.fetch/2` and `Keyword.put/3`
- [Map] `Map.replace/3` is deprecated in favor of `Map.fetch/2` and
  `Map.put/3`
- [Macro] `Macro.unescape_tokens/1` and `Macro.unescape_tokens/2` are
  deprecated in favor of `Enum.map/2`
- [Range] Deprecate `Range.range?/1` in favor of pattern matching on
  `_ .. _`