Python 2 code cleanup

[michael-etzkorn]

@Paebbels brought up a couple of good issues in #4 that are present in main.

• Python 2 class style declaration class VhdlObject(obect): should be class VhdlObject: (fixed in VHDL parser from andres manelli's fork for entity parsing support  #4)
• Use of .format instead of f"" (fixed in Python 2 to 3 migration changes: format strings #6)
• os.path.splitext(fname)[1].lower() in ('.vhdl', '.vhd') should use pathlib instead

Finally, while not directly Python 2 related. There's the issue of Sphinx's parsing of arguments for documentation:

• Args: should be :param [ParamName]: See Writing docstrings - Sphinx-RTD-Tutorial