Introducing: 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 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 read more about plugins in the documentation.

For homebrew users:

I will keep up-to-date homebrew formulae for all plugins I'm aware of in this repository.

You can access this formulae with the following command:

$ brew tap pote/gpm_plugins

After this you can just install them as you would any other package

$ brew install gpm-bootstrap

Plugin Example: gpm bootstrap

Looking forward to seeing new plugins pop up! 📦 🎆