http://wiki.geda-project.org/geda:gschem_symbol_generators

http://wiki.geda-project.org/geda:tragesym_tutorial
http://www.gedasymbols.org/user/dj_delorie/tools/djboxsym.html
https://github.com/setarcos/gmk_sym
http://turkos.aspodata.se/git/openhw/pdftosym/pintosym.pl