docs: fill out and clean up Version page a little - #1089

Working on the Version page a little:

• Drop the __weakref__ display on packaging.version.InvalidVersion
• Document from_parts, __replace__, __match_args__
• Override the __replace__ signature to be more useful
• Display the __replace__ parameters
• Add versionchanged and versionadded
• Trick sphinx into putting versionadded in the right place (at the end) of from_parts by including at least one :param ...
• Mention fast path replacements for .public and .base_version
• Mention that parse(...) is identical to Version(...)