Add python api document

[mh-northlander]

#98

Generate doc:

• install sudachi.rs python binding: pip install setuptools-rust; python setup.py develop
• install sphinx and theme: pip install sphinx sphinx-rtd-theme
• run make html in docs directory
  • html will be generated under docs/build/html

[eiennohito]

Please don't add automatically-generated things to git.

Also, does the build generate .pyi files like https://github.com/huggingface/tokenizers/blob/master/bindings/python/py_src/tokenizers/__init__.pyi?

[mh-northlander]

.rst files are contents files to auto-generate documents with sphinx. We can write additional explanations to them.

Also, does the build generate .pyi files like https://github.com/huggingface/tokenizers/blob/master/bindings/python/py_src/tokenizers/__init__.pyi?

Those pyi files are generated by https://github.com/huggingface/tokenizers/blob/0fe9214f44f4e117a85e3880c20631cc70298d86/bindings/python/stub.py.