Feature/diagnostics

A flexible, event-based runtime diagnostics component.

Full documentation available in `docs` folder:
https://github.com/Thinkscape/ZFTool/blob/feature/diagnostics/docs/DIAGNOSTICS.md

I've decided to implement Diagnostics as a feature of ZFTool (as opposed to ZF2) because it depends on configured MVC to gather definitions from config, other modules and then run tests. Despite that, `ZFTool\Diagnostics` can easily be used standalone, extended and augmented (with EM listeners).