Log Message:
py-meld3: updated to 2.0.0

2.0.0:
- Removed support for older Python versions.  On Python 2, meld3 now
  requires Python 2.7.  On Python 3, meld3 now requires Python 3.4 or later.
- Added Python 3.7 classifier to ``setup.py``.  No code changes were
  needed for Python 3.7 compatibility.