[wip][rfc] shell version(posix compatible)

This a working progress implementation.

goals:
 - remain posix compatible(aka: work with most shells(zsh and bash top priority)
 - mimic all current lunchy features
 - integrate with homebrew(easy install)

that said, I'm open this PR as a request for comments.

I will work in the Easter holiday in it and I expect to have a almost 100% compatible version next weekend.

@mperham: what do you think?

anyway, Thanks a lot for lunchy, it's a time saver!