docs: Add documentation to a subset of available extensions

[rscarson]

I was able to use my experience with some of the Deno extensions to flesh out their documentation a bit

I've provided docs for the following:

• web
• fetch
• net
• webidl
• url
• io
• crypto
• console

The only code change I have made is to formalize the previously undocumented dependency between deno_io and deno_tty

I do plan to eventually add support in my own crate for all deno extensions, and plan to document them as I get through them

If there are internal guidelines for documentation which I am not adhering to, I will happily modify these to match them

[CLAassistant]

All committers have signed the CLA.

[crowlKats]

i am in favour of making the documentation more expansive, however having the ops seems a bit much, as these will most likely get out of date

[rscarson]

i am in favour of making the documentation more expansive, however having the ops seems a bit much, as these will most likely get out of date

deno_net already provided such a list, I tried to match that

Also to be fair, most documentation goes out of date on a regular basis, especially with APIs that change as quickly as this one

I expect a lot of the JS side to change often too, like the change to move timers away from deno_web for example

[rscarson]

Linter has now accepted the formatting; unsure why checks are still failing

[rscarson]

Adjusted pr title as per lint

[bartlomieju]

LGTM, thanks!