Replace vcs_info precmd with vcs_prompt_info

* vcs_info precmd breaks terminal when resuming suspended interactive
  jobs (e.g. in python, irb pressing return results in ^M)
* Rewrite vcs_prompt_info plugin to only support git branch names
Add rbenv.zsh and z.zsh plugins
Cleanup zshrc and zsh/lib files
Plugin updates
Fix git and OS X unicode filename mismatch