Local project source in Godeps

[zankich]

Adds the ability to specify local source directories in the Godeps file.

The source can either be a relative path to a source directory or an absolute path on the file system

myrepo.com/my/project .
myrepo.com/my/awesomeProject ../awesomeProject
myrepo.com/my/otherProject /path/to/my/otherProject

[zankich]

There will be a merge conflict with #26, which I can resolve if this pull request is accepted first.

[zankich]

I merged this branch into #26 and resolved the merge conflicts.