Basic Perforce provider

Should look and feel like the other SVN/HG/etc... providers.  I had to add a few Perforce specific parameters and support for Workspaces.  I may need to enhance the use of Workspaces later, but this should get most Perforce users started.
Could you update https://github.com/puppetlabs/puppetlabs-vcsrepo#parameters with any new parameters too?