some grammar/punctuation mistakes

bugfix: git_ahead no longer reports 'none' as 'ahead'

git_ahead: Rewrite code, fix ahead being reported as behind

registry: Add lolfish theme

registry: add hasanozgan/theme-lambda

Update theme docs (Themes.md)

registry: add rafaelrinaldi/theme-pure

This updates omf plugin to new architecture, moving
functions to `functions` directory. It also revamps the
separation of concerns between CLI and underlying
implementations, organizing them into directories,
whose are autoloaded in plugin startup.

Remove update instructions

Oh My Fish has been stable for many months, we no longer need the update
instructions on the main README.

Update package: fasd

Note for fasd:

Existing fasd plugin doesn't even work properly.

- No fasd_cd
- No default aliases (f, a, s, d, z, zz, ...)

So I forked it and totally rewrote it. Please consider it as different
plugin.

New theme: shellder

Shellder is a fork of agnoster, with smarter functionalities

Fix issue #197: quote OMF_PATH

Support omf- prefix for packages

bugfix: add missing $s in variable tests in git_ahead.fish

Run tests on osx

Unfortunately we can't use docker anymore in order to support automatic
build on OSX.

Better test output

OSX `date` does not support milliseconds output, so @derekstavis created
this `C` code to generate the time with milliseconds.

Show name of the test that failed with the failure message.