initial PR for docs

[HajimeKawahara]

addresses #4

to compile the sphinx doc, at jkepler

python setup.py install
rm -rf documents/jkepler
sphinx-apidoc -F -o documents/jkepler src/jkepler
cd documents
make clean
make html

See documents/_build/html/ The sample is https://secondearths.sakura.ne.jp/jkepler/

If you prefer Readthedoc to the local server, make the account.