refactor(commands): move install action to a qualified function

done the same with freeze, as it'd end up having the same name
refactor(install.go): refactor action install

split megamoth action into separate functions
feat(readme): add freeze and install info
feat(install): use goroutines to install

modify install to launch a goroutine for each ```git clone``` it has to
perform.
Merge pull request #7 from pepegar/feature/install_goroutines

use goroutines for installing vkgrc plugins