documented else / finally syntax for try / catch
Merge pull request #202 from paultag/paultag/feature/start-language-lib

Add in a language lib.
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.