Add PATCH HTTP verb

[nickpellant]

This allows rack-client to perform patch requests. If the code is acceptable to the core maintainers I'd like to get this merged & tagged so that I can submit a pull request to engineyard/ey_api_hmac for a version bump.

[halorgium]

@nickpellant seems good. I'll get master passing again. The new rspec 3 release has broken the build.

[nickpellant]

@halorgium I think I know what the problem is, can push a fix to this PR for you?

[halorgium]

@nickpellant would you be able to push a new PR getting master green?
I had some other issues:

• https://github.com/halorgium/rack-client/compare/lock-rspec-below-v3
• https://travis-ci.org/halorgium/rack-client/builds/34722625

[nickpellant]

@halorgium The build passed: https://travis-ci.org/halorgium/rack-client/jobs/34722494

Not sure why it's coming through as not complete on here.

[nickpellant]

Looking at the build @halorgium it's failing due to the test suite being run against JRuby and RBX.

[halorgium]

@nickpellant ah, I see you've pushed your PATCH to your master branch.
I generally try to have my forks exactly track the upstream, so if situations like this arise, I can branch off of a clean slate.

I'd like to get the tests green again without your PATCH patch, for clarity.
Could you branch off of halorgium/rack-client@master, file a new PR and get the tests passing?

Thanks!

[nickpellant]

@halorgium Take a look at #19 for work on fixing the build.