Road to v2.0

Based on the changes by @patbenatar I started iterating towards v2.0, this is the current WIP. Personally, I think it got much more cleaner, more readable, more extensible and generates fewer methods. Due to this some parts will be not be backwards compatible.

- [ ] Make validations work
- [ ] Support transforms like `strings: true` did previously, still required/useable?
- [ ] Clean up specs, remove obsolete specs etc.
- [ ] Add mongoid support, should be trivial in fact
- [ ] Finish new README
- [ ] Update gh-pages... maybe find a designer for a neat logo

/cc @the-robear