concatenate edge "links" attributes for multigraphs
Allow merging link attributes which have links:
linkattrs1 = {"source": "A", "target": "B", links=[adict1]}
linkattrs2 = {"source": "A", "target": "B", links=[adict2, adict3]}
linkattrs_merged = {"source": "A", "target": "B", links=[adict1, adict2, adict3]}
Edited by Wout De Nolf