docs: put html-only table of contents into developer guide
docs: put html-only table of contents into developer guide

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