update usage docs (#1270)

[gurgeous]

Took a stab at rewriting the Usage page. Changes include:

1. showing method signatures for HTTP verbs
2. give an overview of adapters & middleware
3. explain a bit more about the shortcut methods vs. creating a connection
4. use httpbingo.org instead of the defunct sushi.com
5. quick note about the default connection and url encoding

I have no ego about this change, feedback is appreciated.

[olleolleolle]

These are wonderful changes, thank you!

When I read "resp" I thought I'd like the full word to be in the variable name, and when I read "bacon" I thought that we could spell it out fully as "chunky bacon" in order to honour _why the lucky stiff properly.

(But those are minor quibbles, easily changed later, if ever.)

I am glad we got to here: you filed an issue which became a discussion, which opened our eyes to starting troubles which could trip first-time users. And, now you have them covered, with this very-valuable PR.

[gurgeous]

Aww, thank you for the kind words! Happy to help. We all gotta stick together in our little community.

[olleolleolle]

@gurgeous Thanks again!

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