Merge pull request #16 from dlecocq/master

Use the libYAML version of yaml if it's available
Update README / version bump for new libyaml feature
Substantial refactoring

This refactoring includes some PEP-8 compliance changes, as well as some more
complete testing to ensure that we're in fact serving everything out of
cassettes when we thing we are.

Incidentally, it also includes fixes for #3 and #4