cleanup source directory

There is o need to keep pkg/ in source control, that's what tags are
for. With puppet_spec_helper now providing all of the functionality in
Rakefile we can safely remove that code. By adding .fixtures.yml we can
also remove most of spec/spec_helper's code.

Finally, we allow ourselves to be a little bit more ignorant: pkg/,
spec/fixtures (managed by puppet_spec_helper) and vim swap files.