Log Message:
Update erlang to 18.0.

- Starting from 18.0 Erlang/OTP is released under the APL 2.0
- erts: The time functionality has been extended. This includes a new API
  for time, as well as "time warp" modes which alters the behavior when
  system time changes. You are strongly encouraged to use the new API
  instead of the old API based on erlang:now/0. erlang:now/0 has been
  deprecated since it is a scalability bottleneck.
- erts: Beside the API changes and time warp modes a lot of scalability
  and performance improvements regarding time management has been made
- erts: The previously introduced "eager check I/O" feature is now enabled
  by default.
- erts/compiler: enhanced support for maps. Big maps new uses a HAMT
  (Hash Array Mapped Trie) representation internally which makes them more
  efficient. There is now also support for variables as map keys.
- dialyzer: The -dialyzer() attribute can be used for suppressing warnings
  in a module by specifying functions or warning options.
- ssl: Remove default support for SSL-3.0 and added padding check
  for TLS-1.0 due to the Poodle vulnerability.
- ssl: Remove default support for RC4 cipher suites, as they are consider
  too weak.
- stdlib: Allow maps for supervisor flags and child specs
- stdlib: New functions in ets:
  - take/2. Works the same as ets:delete/2 but
            also returns the deleted object(s).
  - ets:update_counter/4 with a default object as
            argument

Full changelog:

  http://www.erlang.org/download/otp_src_18.0.readme