The requirements are cross-referenced to dedicated page, similarly to
TODO and bug lists.
Also updated / improved documentation for some texture / image formats.
* For libraries that are part of the same project using directly target
name instead of ${*_LIBRARY} variable.
* Prefixed test target names with namespace, so tests for the same
class in different namespaces won't conflict.
* Removed unneeded linking to ${CORRADE_UTILITY_LIBRARY} in some
places.
Now the data type is part of attribute definition, so user doesn't have
to guess / look up what data should be there when binding with
Mesh::bindAttribute().