Since plugins are under their own directories, the /plugins/foo/foo.plugin.zsh
naming scheme is redundant.
Naming the entry point of plugins init.zsh will encourage the splitting of
large plugins into multiple files.
Merge completion with official brew completion. Add a helper to link official
completion into oh-my-zsh plugin (without overwriting). Add an alias to list
installed brews. Add brews to the path (in a somewhat strange way).
