Add support for cargo features

[Eijebong]

I just mirrored the cargo build option within the rls config struct.

For some reasons I have some tests writing to stderr, I can't figure out where this is coming from. I don't know if it's a problem in my tests or not.

[Xanewok]

Hi, thanks for the PR!

Regarding the tests and stderr, it's reported (#393) and I wouldn't worry about that.

It'd be good to also include the additional "rust.{...}" configuration for that on the rls-vscode side. Would you mind also filing a PR there with the added configuration options?

[Eijebong]

Done :)

Edit: Ow, tests have changed, I'll rebase properly tomorrow

[Eijebong]

Build failure seems to be unrelated

[Xanewok]

@Eijebong could you try closing and re-opening to redo the CI build?

[Eijebong]

@Xanewok Rebased and pushed. It didn't work. Do I have to open another PR for appveyor to throw away its cache ?

[Xanewok]

Not sure how AppVeyor cache works exactly, but if it's gonna refresh on another PR, doesn't hurt to try.
In general AppVeyor has some hiccups recently wrt the cache, so that in itself might be worth looking into.

[nrc]

@Eijebong there is still (or perhaps again?) a merge conflict, so I think this needs another rebase. Lets not worry about Appveyor, as long as Travis is green we can land.

[Xanewok]

AppVeyor cache was purged (#510), so ideally it should also be green now, after rebase, too!

[Eijebong]

Rebased

[Xanewok]

🚥 All green now, thanks!