gen_gallery.py: new generate_rst_files()
gen_gallery.py: new generate_rst_files()

- new _get_fig_filename(), _make_sphinx_path()
- update generate_images(), main()
- initial working version

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