Core stability

- Core fs_* methods now return errors
- lcore.platform is now properly determined and not assumed to be love
- base_directory property added
- errors now default to "unknown error" as to not crash with an
unhelpful message if none is given.
- Fix straggling call to love.filesystem.load in L::load
- Return self in all non-loading methods for pretty method chaining
Organize feature list
LOVE platform library

Right now, this library just helps setting up event hooks, which saves
quite a bit of code and some debugging headaches. Use it!
Update documentation to latest version