GitLab

* add cuda utils; change g.to; add g.device

* split array.h into several headers

* cuda index select

* file

* three cuda kernels

* add cuda elementwise arith and several others

* cuda CSRIsNonZero

* fix lint

* lint

* lint

* fix bug in changing ctx to property

* address comments

* remove unused codes

* address comments

* add cuda source

* moving codes from kernel2 branch

* operator overloading

* Better error message for unsupported device

* fix c tests

* coo sort using cusparse

* move test_rpc to distributed

* lint

* address comments and add utests
Co-authored-by: Jinjing Zhou <VoVAllen@users.noreply.github.com>
Co-authored-by: Chao Ma <mctt90@gmail.com>
Co-authored-by: xiang song(charlie.song) <classicxsong@gmail.com>