GitLab

* enable cython

* add helper function and data structure for void_p vector return

* move sampler from graph index to contrib.sampling

* WIP

* WIP

* refactor layer sampling

* pass tests

* fix lint

* fix graphsage

* remove comments

* pickle test

* fix comments

* update dev guide for cython build

* include/dgl/runtime

* include

* src/runtime

* src/graph

* src/scheduler

* src

* clean up CMakeLists

* further clean up in cmake

* install commands

* python/dgl/_ffi/_cython

* python/dgl/_ffi/_ctypes

* python/dgl/_ffi

* python/dgl

* some fix

* copy right