Trac #16972: Moved code to read planar code to separate method
Trac #16972: Extended documentation of _read_planar_code
Trac #16972: Use the new _read_planar_code method in fullerenes and fusenes.
Merge changes of #16972 into this branch
#16970: Adding method to generate plane graphs
#16970: Adding method to generate plane triangulations
#16970: Changed formation of command
#16970: Added method to generate quadrangulations