New: dev: basic support for multi-edges for gh-211
chg: dev: more parallel link support for gh-211
Chg: dev: phase one of interface->port for gh-218
chg: dev: more work on interfaces -> ports for gh-218
Chg: dev: physical_interfaces -> .physical_interfaces() for gh-197
Chg: Dev: restore searching for edge by (src_node, dst_node)
Chg: dev: Use layer3 for gh-206
Chg: dev: tidy, remove pickle methods
Chg: dev: more work on parallel links, interfaces for gh-218 and gh-211
chg: dev: more work for gh-211 gh-218
Fix: dev: bug in the new add_edges_from code
Chg: dev: Allow setting of kwargs for edges
Chg: dev: remove node.phy -> use node['phy']
Chg: dev: Use n.loopback_interfaces() instead of n.loopback_interfaces for gh-197
Chg: dev: tidy @minor
Chg: dev: rename type to category for interfaces/ports for gh-218
chg: dev: work for gh-220
chg: dev: tidy
chg: dev: improving support for parallel edges gh-211
Chg: dev: more work for gh-201