----------------
- Remove relative directory resolving.
[rnix]
- Add ``remove`` function to ``ResourceMixin``.
[rnix]
- Add ``copy`` function to ``ResourceMixin``.
[rnix]
- Add ``scripts``, ``styles``, and ``links`` properties to ``ResourceGroup``.
[rnix]
- Introduce ``parent`` attribute on ``ResourceMixin``. Gets set in
``ResourceGroup.add`` method to provide hierarchy information.
[rnix]
- Remove magic path resolving behavior for resources. Path no longer gets
overwritten in resolver. It gets now aquired from parent if not set on
resource or resource group.
[rnix]
- ``LinkResource`` and ``StyleResource`` have common superclass ``LinkMixin``
now. ``StyleResource`` no longer derives from ``LinkResource``. This way,
link and style resources respective subclasses of it can be differentiated
with ``isinstance``.
[rnix]
- Remove ``sizes`` keyword argument from ``StyleResource`` constructor.
[rnix]
- ``ResourceGroup`` can define a directory for contained resources.
[rnix]
- ``Resource.directory`` no longer gets set to package path by default but
remains ``None``.
[rnix]
- Resources can define multiple dependencies.
[rnix]