Replaces http.server with Tornado

[vasinkd]

fixes #1189

[tsnoam]

Thanks. We'll check this out.

[vasinkd]

Sure. Thank you for supporting this great library! BTW, I didn't spend time on fixing of tests since you may still decide to fix this issue with http.server, just made minimal working solution.

[vasinkd]

Ok. I guess it is almost the final version.

This code can be executed with Python 2.7, Python 3.4+ and (probably) PyPy.
It fixes #1189

Now it returns a little different HTTP status codes: 500 (used to be 403) if Content-Length header is not readable and 404 (used to be 200, why?) if someone uses not POST-request or incorrect URL. It may be easily changed if necessary.

Also, SSL-Certificate check is provided by ssl_ctx.load_cert_chain(cert, key) which has OpenSSL under the hood. I removed _check_ssl_cert function in favor of this method.

I didn't understand what to do with tests aimed at Telegram API 4.0 coverage. Should I comment them out?

[tsnoam]

@vasinkd Thanks. I'm on vacation until next week so I will be able to properly review the code only then.

Regarding the API unitests, just ignore them for now.

[vasinkd]

@tsnoam Ok. I'll leave the code as it is until you review it.
Enjoy your vacation!

[tsnoam]

Sorry for the delay.

1. I like it. IMHO, we should get this solution into the library.
2. We'll need to work on py2.7 compatibility. Specifically I think we should use the Tornado eventloop (instead of asyncio's).
3. I merged latest master and pushed. Lets see which unitests pass and which needs to be fixed.

[tsnoam]

@vasinkd
Thank you very much for this contribution.

[vasinkd]

I believe that I found out that answer 200 for GET request was there for a reason :)
Actually, get_webhook_info will always return an error with the code above.

[vasinkd]

I added a fix to the branch "vasinkd:tornado_webhook".
Should I open a new PR?

[tsnoam]

@vasinkd yes please