Adds compilations functions to pillar.

- new `pillar-compile-to-FORMAT' functions
- adds a makey popup to `pillar-mode-map' for compiling files
Do not add newlines in function documentation.
Renames `pillar-executable-path` to `pillar-executable`
Merge pull request #4 from NicolasPetton/master

Adds support for compilation from within Emacs