make sure $PATH is setup first
Source all path.zsh files in the project before the rest
Improve zsh file sourcing.

Now it gets all of the files once, then iterates over three times,
once for path, once for general stuff, once for completion
update the README for special handling of path.zsh and completion.zsh
unset config_files after sourcing everything
Merge pull request #66 from rcarver/source-path-first

make sure $PATH is setup first