Add take-headers methods for incoming messages and bump package version to 0.2.1-draft

[acfoltzer]

Closes #102. See discussion in that issue for the motivation and design of this change.

[lukewagner]

I'm not sure we need to mark consume as deprecated in 0.2.1 -- if all you want is to do is read the body stream, it's a reasonable method to call (and perhaps a bit more efficient; not forcing you to copy strings you don't want). Note that 0.3 is free and expected to make big breaking changes, and if you check out #101, you can see a sketch of how it might look.

[acfoltzer]

Removed these notes in 55a4754

[lukewagner]

Looks good to me. It'd be good to hear if this makes sense to others too.

Assuming it does, before merging, we'll need to answer the process question of how we want to manage post-0.2 additions in the WIT in the individual proposal repos post-0.2. I forget what we settled on. In particular, once the contents of the proposal repo no longer match what's in the 0.2 snapshot in the wasi repo, should we first change all the versions in all the WITs in this repo to something other than 0.2.0, say, 0.2.1-ephemeral, so that we're not falsely claiming that our take-headers is part of 0.2.0?

Any thoughts @sunfishcode @ricochet @pchickey?

[pchickey]

I believe we should change the version to be 0.2.1-draft as part of this PR.

[acfoltzer]

@pchickey I'm guessing we'll want to stick with 0.2.0 for the dependencies for now, and just change to package wasi:http@0.2.1-draft in proxy.wit?

[pchickey]

Yes, we should only change the version at the wasi:http package declaration in proxy.wit.

[acfoltzer]

Got it; updated the version and also edited the PR title to better reflect the new approach

[acfoltzer]

Unsure why the CI check is failing here; I have wit-bindgen-cli 0.17.0 installed as does the Actions script, but the --check test is failing on the output I've produced.