Update scripts/changes.py for BEP 1.

Prints out change log using new format that leverages BEP 1 changes.
Also adds a check mode which validates issues against BEP 1
requirements.
Merge pull request #1050 from lexicalunit/mattpap/filter_issues

Update scripts/changes.py for BEP 1.
Merge remote-tracking branch 'origin/mattpap/filter_issues'