Adopt Epydoc's DottedName class

[tristanlatr]

Probably it would be good to have this level of abstraction for name handling.

This is the test code of the DottedName class.

The attractiveness comes from the contextualize() method:

>>> DottedName('foo.bar.baz.qux').contextualize(DottedName('foo.bar'))
    DottedName('baz', 'qux')

This would help contextualize the names when we need, to avoid stuff like this (This is in #414):

It could also help figure a standard way of showing the names and solve #280

What I propose here is to edit some stuff a follow:

• The core of the change: Documentable.expandName(name:Union[str, DottedName]) -> DottedName
• Create Documentable.fullDottedName() -> DottedName
• Refactoring:
  • node2dottedname(node:Optional[ast.expr]) -> Optional[DottedName].
  • node2fullname(node:Optional[ast.expr], ctx: model.Documentable) -> Optional[DottedName]
  • System.objForFullName(fullName: Union[str, DottedName]) -> Optional[Documentable]
  • System.find_object(full_name: Union[str, DottedName]) -> Optional[Documentable]
  • CanContainImportsDocumentable._localNameToFullName_map: Dict[str, DottedName]
  • CanContainImportsDocumentable._localNameToFullName(name: str) -> DottedName
  • All code that use those objects