Add new helper for request param matching on a regEx

[mcarti]

New Issue Checklist

• [x] I have tried with the latest version of OHHTTPStubs
• [x] I have read the README
• [x] I have read the Using the right Swift Version of OHHTTPStubs for your project section
• [x] I have searched in the existing issues
• [x] I have read the OHHTTPStubs wiki to see if there wasn't a detailed page talking about my issue

Environment

• version of OHHTTPStubs: 8.0.0
• integration method you are using:
  • [x] Cocoapods
  • [ ] Carthage
  • [ ] submodule
  • [ ] other
• version of the tool you use: [INSERT VERSION HERE]

Issue Description

Not an issue but a proposition of a new helper. I use your library for testing my project and I thank you very much, it's very usefull. For our project needs I've written a new helper I called 'containsQueryParamsMatching'. Whereas the existing helper 'containsQueryParams' matches on query parameter string value equality, 'containsQueryParamsMatching' matches on query parameter matching a given RegEx. I'm ready to make a PR if you think this helper is usefull.

[jeffctown]

@mcarti - yes, a PR would be great!