improve gen_gallery.py
improve gen_gallery.py

- add captions, contents and section titles

sfepy/sfepy,RexFuzzle/sfepy,sfepy/sfepy,lokik/sfepy,sfepy/sfepy,BubuLK/sfepy,lokik/sfepy,lokik/sfepy,rc/sfepy,rc/sfepy,vlukes/sfepy,RexFuzzle/sfepy,rc/sfepy,BubuLK/sfepy,RexFuzzle/sfepy,vlukes/sfepy,vlukes/sfepy,BubuLK/sfepy,RexFuzzle/sfepy,lokik/sfepy