script/gen_release_notes.py: fix for Python 3, improve formatting
script/gen_release_notes.py: fix for Python 3, improve formatting

vlukes/sfepy,BubuLK/sfepy,sfepy/sfepy,vlukes/sfepy,vlukes/sfepy,sfepy/sfepy,sfepy/sfepy,rc/sfepy,rc/sfepy,BubuLK/sfepy,BubuLK/sfepy,rc/sfepy