* trying to refactor IndexSelect
* partial implementation
* add index select and assign for floats as well
* move to random choice source
* more updates
* fixes
* fixes
* more fixes
* adding python impl
* fixes
* unit test
* lint
* lint x2
* lint x3
* update metapath2vec
* debugging performance
* still debugging for performance
* tuning
* switching to succvec
* redo
* revert non-uniform sampler to use vector
* still not fast
* why does this crash with OpenMP???
* because there was a data race!!!
* add documentations and remove assign op
* lint
* lint x2
* lol what have i done
* lint x3
* fix and disable gpu testing
* bugfix
* generic random walk
* reorg the random walk source code
* Update randomwalks.h
* Update randomwalks_cpu.cc
* rename file
* move internal function to anonymous ns
* reorg & docstrings
* constant restart probability
* docstring fix
* more commit
* random walk with restart, tested
* some fixes
* switch to using NDArray for choice
* massive fix & docstring
* lint x?
* lint x??
* fix
* export symbols
* skip gpu test
* addresses comments
* replaces another VecToIdArray
* add randomwalks.h to include
* replace void * with template
* fix lint for graph_index.py
* pylint for base.py
* pylint for batched_graph.py
* pylint for frame.py; simplify and fix bugs in frame when index is slice type
* pylint for graph.py
* pylint for immutable_graph_index.py
* pylint for init.py
* pylint for rest files in root package
* pylint for _ffi package
* pylint for function package
* pylint for runtime package
* pylint for runtime.ir package
* add pylint to ci
* fix mx tests
* fix lint errors
* fix ci
* fix as requested
* fix lint
peizhou001