Autoclass

* Added `on_each_` and `on_all_`

* `lts` was erroneously mappend onto `gt`. Fixed this.

* New decorator `autoclass` to apply several features at once.
* `autodict` now also generates a `from_dict` static method in the class, as well as `__str__`, `__repr__` and `__eq__` if not present

* New decorator `autodict` to make a class behave like a (read-only) dict. So this is a 'dict view' on top of an object, basically the opposite of `munch` (that is an 'object view' on top of a dict)

* better error messages for set enforcers
* uniform management of validators lists: now passing a list creates an 'and_' operator behind the scenes
* better handling of empty lists
* and, or, xor now automatically replace themselves with their contents when their contents is a single validator
* added a few tests to improve coverage (hopefully)

* better validation error messages for parametrized validators