GitLab

* Implement all extension building in main setup.py

* Remove old build files

* Adapt installation guide

* Refactor to comply with flake8

* Move imports into functions & refactor module paths

* Format setup.py with yapf

* Move cython/numpy import back to head of file

* Add note to use verbose mode for pip in INSTALL.md

If you are not export a directory that contains the "activate" file to $PATH, it will show "activate: No such file or directory".
So conda activate is more preferable.

* update installation guide

* fix typo

* update conda python version from 3.6 to 3.6