Make a prettier documentation

[Cloudac7]

Now the documentation was implemented through mkdocstring. It is just a simple test for existing docstring. However, the documentation now is so poor that nobody could actually execute analysis with only these files. Therefore, a lot of work should be finished.

• Fix most docstring for exsiting functions and classes
• Make all docstring to the same style (We might just use the Google one)
• Write a easy usage
• Other things to be done