Merge pull request #11 from esacteksab/docs

this makes more sense I think
Abide by the documented API

- You could not pass in `match_requests_on` in Betamax#use_cassette
Update HISTORY.rst
Fix #10
Fix python 2.6
Fix documentation
Try to catch a regression
Failing test
Fix URI matching issue

Closes #18
More elegant solution in matchers

Start using a hook for initialization so that users can customize how their
matcher object behaves on initialization. Undocumented right now, but it will
be documented.
Add documentation for on_init

Closes #20