Updating NEWS entries.
Move code from hy.readline_helpers into new hy.completer.completion context
manager so we can "wrap" readline completion around REPL interaction.
documentation for some of the builtins
references #18
Style fixes.
Merge branch 'master' into pr/222
Jank @olasd's hack, clean up core.

 The core shall from now on be only for the core language bits. Macro
 bits shall live in hy.macros and in hy.compiler. This cleans up
 garbage.