* WIP: using object system for graph * c++ side refactoring done; compiled * remove stale apis * fix bug in DGLGraphCreate; passed test_graph.py * fix bug in python modify; passed utest for pytorch/cpu * fix lint * address comments
* refactor. * accelerate update_all in nodeflow. * fix. * refactor. * fix lint. * fix lint. * reorganize. * reorg. * remove. * add doc. * impl block_incidence_matrix * fix lint. * fix. * simple fix. * fix test. * fix interface. * fix eid. * fix comments.