GitLab

Updated _brew to match latest in https://github.com/Homebrew/homebrew/blob/master/Library/Contributions/brew_zsh_completion.zsh

`brew services` and `brew server` were moved to homebrew-boneyard.

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).

- update plugin architecture
- completion function in $ZSH/functions/brew
- plugins/brew.plugin.zsh only activates