support compounding expectations

Currently, the `Have` matcher doesn't support [compounding expectations](https://www.relishapp.com/rspec/rspec-expectations/docs/compound-expectations) with `RSpec::Matchers::Composable#and`, which is functionality new to RSpec 3.x. 

This PR includes the `RSpec::Matchers::Composable` module in your custom matcher so we could compound with the mixin method. I've also added 3 unit tests, so see those for a simple example of compound expectations in action.
it'd be good to make this more descriptive, e.g. `it "passes when all the expectations are met"`