* multigraph support on graph index
* more tests
* multigraph flag, bugfix on clear & copy
* networkx interfaces
* including graph index tests in Jenkins
* node subgraph test
* edge subgraphs
* removing duplicates in pred/succ
* more explicit test and doc
* query source and destination from edge id
* subgraphindex
* renaming has_edge to has_edge_between, apply_edges adding eid
* send_on and send_and_recv_on
* DGLGraph edge subgraph
* merged send_on and send_and_recv_on
* change request
* removing hashmap
* creating multigraph by flag; mingw support
* changes per request
* reverting networkx auto multigraph discovery
* notes on send/send_and_recv on multigraphs
* changing test reducer from sum to max
* added a fixme note in spmv scheduler
Gan Quan