Http Methods handling to look more like requests

Allow users to specify methods via the same HTTP method based format
that requests does. It makes them look more synchronous.
Add period to error message

Looks better as there is already one period in there.
Make matcher public
Return Matcher from register_uri

Return the matcher we added with register_uri. Add some methods to test
if the matcher has been called. Make everything else private.

The idea is that after you've registered your matcher you should be able
to take the return value and test if that matcher was ever called.