* update tree lstm
* tree_lstm (new interface)
* simplify pop
* merge qipeng(root)
* upd tree-lstm & tutorial
* upd model
* new capsule tutorial
* capsule for new API
* fix deprecated API
* New tutorial and example
* investigate gc problem
* add viz code
* new capsule tutorial
* remove ipynb
* move u_hat
* add link
* add requirements.txt
* remove ani.save
* update ci to install requirements
* utf-8
* change seed
* graphviz requirement
* accelerate
* little format
* update some markup
* add examples in traversal.py
* message propagate methods
* use the new message propagation for tree-lstm
* update to the new name
* update propagate API doc
* update doc
* add propagate utest
* WIP: API renaming
* API rewrite and node function refactor
* builtin functions
* builtin functions tested
* fix test
* send and recv spmv test
* WIP: fix examples
* Fix examples using new APIs