!!! c4dtools.prepare() interface change

Changed parameter names:

- use_cache => cache
- parse_descriptions => parse_descriptions
/// no changes
Added __getitem__ to Resource class

c4dtools.resource.Resource.__getitem__(<item name>) is a shortcut for
~.string.<item_name>
Enhancements, moved code

- moved ~.func_attr to c4dtools.decorats, now named f_attrs (backwards
compatibility remained, will be removed in 2.0.0)
- added ~.get_real_descid()
- added ~.iter_inexclude()
- extended ~.AtomDict class by
+ __copy__()
+ __deepcopy__()
+ __len__()
+ clear()
+ copy()
New sub-module: c4dtools.decorators

Added new module c4dtools.decorators.

- @f_attrs, previously known as c4dtools.utils.func_attr
- added @override and @subclass, only useful in combination