tests improved, verify added

I improved a little bit tests and introduced `codeception/verify` extension. This extension is just simple wrapper against some very used asserts. The main benefits we get:

1. Increases readability of tests, and writing of it.
2. It is more likely and almost often so, that user first think about specification (to be simple, message that goes first), and only then perform some assertions. So users will not be reading first assertions and only after that reading expectation message.
3. As it simple wrapper over some asserts id does not touch some internal logic or smth. like this, and all phpunit assertions can be used by developers as they want. This is just simple syntax sugar.
4. As you would look into ruby rspec/minitest they do it similar: first goes message, then assertions.

I think it can be merged, because for end-user it is more friendly and readable, so they can start playing around with tests with some fun :)