Log Message:
Update to 1.12.1

changes:
1.12.1
 - Added ToJSONFilter instances for a -> [a], a -> IO [a].
     These use generics and will be slower, but are needed for
     backwards compatibility.
1.12
 - Generic: Removed deprecated processWith, processWithM
 - Made setTitle, setAuthors, setDate non-polymorphic. 
 - Generalized docTitle, docDate, docAuthor so they work with MetaBlocks.
     This will help with MMD title blocks, where the fields parse as
     MetaBlocks [Plain ils].
 - Walk: Added instance for Walkable a [b].
 - Walkable instances for Pandoc Pandoc and Meta Meta.
 - Switch to left-biased union for mappend of Meta.
 - Monoid instances for Pandoc, Meta.
 - Builder: plain now produces mempty on empty input.
 - Use a derived Show instance for Format.
 - IsString instance for Format.
 - Made Format a newtype.
     It still embeds a string, but comparison is case-insensitive.
 - Changed Text.Pandoc.JSON to use Text.Pandoc.Walk.
 - Added Text.Pandoc.Walk.
 - Added Span and Div generic Inline/Block containers with attributes.
 - Added ToJSONFilter instances to allow use of script arguments.
 - Removed obsolete CPP macros.
 - Added MetaBool to MetaValue.
 - ALlow bytestring 0.10.*.
 - Added JSON serialization/deserialization.
   * pandoc-types now requires GHC generics, hence ghc >= 7.2
   * Text.Pandoc.Definition now derives ToJSON and FromJSON instances
     for pandoc types
   * Text.Pandoc.JSON module exports ToJSONFilter typeclass (a replacement
     for the ToJsonFilter exported by Text.Pandoc, which will soon become
     a deprecated synonym).
 - Definition: Export isNullMeta.
 - Added MetaInlines to MetaValue.
 - Builder: Added deleteMeta method to HasMeta class.
 - Builder: Add HasMeta class (with setMeta).
     setMeta can now be used on either Pandoc or Meta.
 - Use json-like structure for metadata instead of association list.
    - `Text.Pandoc.Definition`:
      + Removed `getMeta` and `getMetas`.
      + Export `MetaValue`, `nullMeta`, `lookupMeta`.
      + `MetaValue` can be pandoc blocks, a raw string,
        or a list or map of other `MetaValue`s.
    - `Text.Pandoc.Builder`:
      + Removed `ToBlocks` type class.
      + Added `ToMetaValue` type class.
      + Removed `setMetas`.  `setMeta` can now be called with a list of values.
 - Made document metadata more flexible.
   * The `Meta` type now takes an association list `[(String, [Block])]`
     instead of three hard-coded parameters for title, authors, date.
   * `Text.Pandoc.Definition` exports new `getMeta` and `getMetas` helper
     functions, plus replacements for the old `docTitle`, `docAuthors`,
     and `docDate`.
   * `Text.Pandoc.Builder` exports new `setMeta` and `setMetas` helper
     functions, as well as a new `ToBlocks` class.