Previous implelmentaiton only worked for a single level tree of dependencies.
This implementations recursively determines the number of levels below a dep_file and uses this value as the key to sort by. The 'dependendency level is cached in the dep_file object to reduce the number of recursive calls.
Will not handle circular dependencies well.

Add architecture to vhdl parser, so that dependencies are generated between the architecture and the entity which may be in different files.
Causes problem in new_dep_solver when entity and architecture are in the same file because now a file will depends on itself (which it technically does). When re-expressing the VHDL dependencies as file dependencies we avoid creating the circular dependency to itself.

Add missing import logging.

Deep modifications of the VHDL parser.