Make raise_for_status chainable

[trim21]

Summary

make it possible to write code like r = httpx.get('...').raise_for_status().json()

Refs #2775

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[abersheeran]

LGTM. It's a small change, but the experience will be much better.

[tomchristie]

Okay great, so...

• CHANGELOG.
• Do we want to mention this usage style in the docstring? In the docs?

[zanieb]

I think this usage should be mentioned in the docstring and prose documentation.

[michaeloliverx]

Really nice DX improvement here, I see myself using this a lot!

[trim21]

document updated
changelog added

[tomchristie]

Looks good. Some minor suggestions...

(Other could also be considered)

[trim21]

is there any ETA on next release?

[tomchristie]

If you're up for helping drive a release pull request, then we could fix up a minor point release whenever really.

[karpetrosyan]

If you're up for helping drive a release pull request, then we could fix up a minor point release whenever really.

Can we include encode/httpcore#745 in the next httpx release?

First, we should release httpcore with that pull request and then release httpx