Added ToJSONFilter instances for a -> [a], a -> IO [a].

These use generics and will be slower, but are needed for
backwards compatibility.
Version bump to 1.12.1.
Made docTitle, docAuthors, docDate work on MetaBlocks [Para].
Version bump to 1.12.2.
Chaged version to 1.12.1.1, as it is a minor bug fix.
Handle MetaString in docTitle, docDate, docAuthors.
Version bump to 1.12.1.2.
Adjusted ToJSON/FromJSON instances for aeson >= 0.6.2.

aeson 0.6.2 changed its default method of deriving ToJSON/FromJSON
instances for generics.  Instead of {"Str": "hi"}, the inline
element Str "hi" was becoming {"tag": "Str", "contents": "hi"}.
This change causes problems for the python pandocfilters module.

This patch uses CPP macros to ensure that the JSON instances work
the same regardless of what version of aeson is used.
({"Str": "hi"}).
Version bump to 1.12.2.
Removed extra #endif.  Thanks to Sergei Trofimovich.
Version bump to 1.12.2.1.
Fixed bug in Walkable Inline Inline / walkM instance for Note.
Version bump to 1.12.2.2.