This commit not only changes the default method of matching requests
(just match on method and URI instead of the entire request + headers)
but also allows the user to add custom matchers.
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
Added support and tests for the Requests library. At least basic
support seems to be working. The tests should run fine if you
don't have requests installed; it just won't verify the requests-
specific tests.
