New RSpec matcher (have_investigated)

[maxlinc]

This adds the have_investigated matcher, which is a more "Pacto-idiomatic" version of have_validated. The difference is that have_investigated matches contracts first, not request patterns, and has more flexibility and better error messages as you apply more and more specific filters.

E.g.:

expect(Pacto).to have_investigated('Echo').with_request(body: hash_including('foo' => 'bar'))
expect(Pacto).to have_investigated('Echo').with_response(body: /foo.*bar/)

You could also write that as a single line if you want to make sure it's for the request and response on the same interaction:

expect(Pacto).to have_investigated('Echo').with_request(body: hash_including('foo' => 'bar')).with_response(body: /foo.*bar/)

Might be possible to simplify further and provide a nice API w/ rspec3, but not sure about keeping it rspec2 compatible.

[coveralls]

Coverage decreased (-3.62%) when pulling 17fc2ad on forensics into b061db5 on master.