Documentation reorganizing

[asvetlov]

aiohttp doc was started from very few pages with relative small content on each.
Now it grows.
Take a look on Client Usage for example: http://aiohttp.readthedocs.io/en/stable/client.html
Endless list of topics in navigation bar and infinite page to scroll on the right.

The same is true for web server docs, the situation is even worse.

The proposal is:

1. Shrink navbar to top livel topics only: client, server, misc (the last is a subject for discussion).
2. Client should contain Client Usage and Client Reference but we need split the Usage into several pages like "Basics", "Cookie Support", "File Sending" etc. I don't know the splitting criteria, it is a hard choice -- but we need it.
3. The same for Client Reference but the splitting is more obvious: ClientSession, request and response, connectors and DNS resolvers.
4. Server part: Tutorial, Usage and Reference, Logging, Low-Level Server and Deployment
5. Others

@aio-libs/aiohttp-committers I need your suggestions and help

[asvetlov]

Partially done.
For future improvements let's create new issues

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a [new issue] for related bugs.
If you feel like there's important points made in this discussion, please include those exceprts into that [new issue].
[new issue]: https://github.com/aio-libs/aiohttp/issues/new