Defer registration until calling requireWithStubs

This removes the need for a callback to be passed to bogus.stub(). But
means that calling bogus.requireWithStubs() is required in order to
properly register the stubbed dependencies.
Remove the dev dependency on Q
Update the readme to use the new stub() API
Merge pull request #3 from aron/refactor-api

Defer stubbed module registration until calling bogus.requireWithStubs()