Allow Matches and ErrorMatches matches to use an already-compiled regexp.Regexp

[pajlada]

This allows users to have full control over the regular expression used for matching.

My use-case was matching a multiline string pattern, and the way MatchString was used in the match-function made that infeasible.

With this change, I was able to use the Matches matcher like this:

c.Assert("asd\nasd", qt.Matches, regexp.MustCompile(`asd.*`))

Happy to update naming of variables on request.
I left naming of parameters/arguments on purpose to keep the diff minimal, but happy to change that too.

As an alternative, if this change is not acceptable, I know I could implement my own Checker handles regular expressions like this, so no worries if this change does not fit into the project!

[frankban]

I think this is an interesting feature.
If you want, please go ahead!

[pajlada]

@frankban I've gone ahead and pushed missing tests for this functionality to maintain the 100% test coverage of checker.go, let me know if you prefer this to be rebased or something before being approved/merged in 🙂

[frankban]

The code looks good!
Could you please add:

• similar tests for ErrorMatches and PanicMatches;
• updated docs for the 3 involved checkers.
  Thanks!

[pajlada]

I added the following tests:
qt.ErrorMatches single-line match expectedNegateFailure
qt.ErrorMatches multi-line match expectedNegateFailure
qt.ErrorMatches multi-line match expectedCheckFailure
qt.PanicMatches single-line match expectedNegateFailure
qt.PanicMatches multi-line match expectedNegateFailure
qt.PanicMatches multi-line match expectedCheckFailure

I added the following documentation:
Added example for Matches checker in checker.go and in README.md
Added example for ErrorMatches checker in checker.go and in README.md
Added example for PanicMatches checker in checker.go and in README.md

[frankban]

Released as v1.14.5