Rmt channels 2

[jneem]

This is a draft to see what it looks like when RMT traits don't have CHANNEL as a generic parameter.

It seems to work, and I think the API is simpler. The one disadvantage is that we can no longer have a type that impls both, say, TxChannel<0> and TxChannel<1>.

Must

• The code compiles without errors or warnings.
• All examples work.
• cargo fmt was run.
• Your changes were added to the CHANGELOG.md in the proper section.
• You updated existing examples or added examples (if applicable).
• Added examples are checked in CI

Nice to have

• You add a description of your work to this PR.
• You added proper docs for your newly added features and code.

[jessebraham]

Sorry for letting this linger for so long. I don't have any strong opinions either way, this looks fine to me. @bjoernQ and @MabezDev can weigh in if they'd like.

If you'd still like to pursue this, would you be able to rebase this and get it to a mergeable state please? Otherwise we can close this for the time being.

[jneem]

Thanks for the reminder, I'd forgotten about this! I don't have a strong opinion either, but I do think it's a reasonable simplification so here's a rebased PR

[MabezDev]

Sorry! This also dropped off my radar, but looks like a nice change. Thanks!

[jessebraham]

LGTM, thanks!