changed pandashp.write_shp signature, added error reporting to match_vertices_and_edges
made pyomotools.read_xls more robust against empty columns and columns full of NaN's
removed lame warning 'column names of indices don't match' from pandaspyomo.get_entities
small doc improvements in skeletrontools; minor post-processing in snappy_endings removes zero-length stubs
small doc improvements in skeletrontools; minor post-processing in snappy_endings removes zero-length stubs