Experimental Plugins

TL;DR: gpm has plugins now, plugins are cool. :)

As can be seen in my ramblings on this pull request there always are certain features which I want to add to gpm but which are not a good tradeoff in regards to functionality/complexity, or do not strictly fall into gpm's responsibility.

That will stop being a problem from now on by introducing gpm plugins, their way they work is pretty simple: if you give an unknown command to gpm it will look for an executable called gpm-<command> in your path and execute that if present, passing along all arguments. The change is introduced in this commit (it's a one liner, I love it) and was suggested by @foca, @inkel and @soveran, to whom I extend my thanks ^_^.

The first released plugin is gpm-bootstrap which takes a look at your Go project, installs all required dependencies setting them to their last release or revision and saves the versions to a Godeps file. Versioning the dependencies of your Go projects has never been easier.

You can see the plugin at work in this example:

Looking forward to seeing new plugins pop up! 📦 🎆