GitLab

* refactor PN SA module code

* refactor PAConv op & add PAConvSAModule

* add unit test

* add PAConvCUDA SA module

* add unit test

* minor fix

* merge master

* move paconv sa modules to a new file

* rename to BasePointSAModule

* rename to PAConvCUDASAModule

* delete typing comment

* refine docs

* rename mlp_spec to mlp_channel

* fix typos in comment