Add Sphinx based documentation

[codingjoe]

fixes #39

[Findus23]

The changes look good, but when I run python setup.py build_sphinx, I get an empty api_docs.html page.
Do I need to run anything else in addition?

[codingjoe]

@Findus23 I am not done yet. The page is empty because there is no documentation. I am writing it right now. Wait for my next commit :)

[Findus23]

Looking really good!

I like the idea of using pylanguagetool as an automated test in CI. I was afraid that it would show too many false positives, but with the whitelist feature it should be possible.

If you are finished, I would merge this. And so that you work won't stay unnoticed, I'll also put the docs online at https://pylanguagetool.lw1.at/

[codingjoe]

Hey @Findus23, I though I was going a bit over board with the personal word list, but I am glad you like it.
I am currently on the run, but I'll try to finish this asap. I also need to do another sorrow review myself.

Regarding publishing the docs, I'd recommend using readthedocs.io, since this then biggest Python open source platform. Plus it builds directly from GitHub, which saves trouble. But you do as you do :)

[Findus23]

No hurry, finish it whenever you find time.

While I see that readthedocs are doing a really great job, I prefer hosting things myself and there aren't that frequent updates that setting up automation is necessarly.

[codingjoe]

@Findus23 I edited the last two commits to accommodate the changes we discussed. Let me know if you want me to change anything else.

[Findus23]

Thanks again for your help, I'll merge it now.

[Findus23]

And the gitlab CI also succeeded: https://git.lw1.at/open-source/pylanguagetool/-/jobs/925