Work on docs for Batman.Object

Splits `docs/03_object.litcoffee` into 4 files:

- `docs/03_object.litcoffee` has API documentation only
- `docs/03a_accessors.litcoffee` has the advice about accessors, plus and minus some stuff
- `docs/03b_observable.litcoffee` has docs for Observable mixin
- `docs/03c_event_emitter.litcoffee` has docs for EventEmitter mixin

great stuff, guys! would love a review when you get a chance.