Adding `gvm linkthis` command

This links the current project into the $GOPATH/src to allow `go get` to
find the local development copy instead of the one on GitHub (or
wherever)

Signed-off-by: Dan Buch <d.buch@modcloth.com>
Merge pull request #31 from modcloth-labs/linkthis

Adding `gvm linkthis` command