Add cross-dev and cross-util commands.

[Alexhuszagh]

The cross-dev command has the target-info subcommand, which target information (libc, compiler, C++, qemu version) for a given target.

cross-dev target-info
cross-dev target-info arm-unknown-linux-gnueabihf

The cross-util command has the list-images and remove-images subcommands. list-images lists all cross images, including local development files. remove-images removes cross images.

cross-util list-images
cross-util remove-images
cross-util remove-images arm-unknown-linux-gnueabihf

Closes #760.

[Alexhuszagh]

I've separated this into many different commits, since this is a large PR and refactors some logic. Each I think is a relatively independent commit, and some of them (such as the removal of the duplicate cpp tags) is crucial for subsequent steps (serde_yaml parsing the matrix).

This also changes the target-info the use Rust rather than bash on the host machine, so the logic is simpler as was mentioned in comment (although using a bash script inside the container still makes sense).

[Alexhuszagh]

Is this better now? I incorporated some of the changes, but thought it would be a bit better to provide a [[bin]] target for cross-dev, since then it can be run easily but disabled by default.

The changes I've made include:

• Moving cross-dev to /cross-dev/main.rs, and using the main Cargo.toml for it. No more Cargo.lock, no more need to not publish it.
• Make cross-dev a [[bin]] target.Since we need serde_yaml as a dependency for it, I've changed it so it's only compiled if the dev feature is enabled.
• engine still uses the same logic. I considered using default_value_t and parse for the clap options, but it was going to be a lot of code and would have probably been less readable than the existing implementation. This is because we'd have to provide a wrapper for which::which, then use default_value_t = cross::get_container_engine().
• Changed the image output to {{.Repository}}:{{.Tag}} {{.ID}}. This is then parsed to an Image (see below). This is because images may be tagged as ${repository}:<none>, which would cause on error on removing the image. Removing it by ID works in this case.
• I've added the --execute flag, so it's a dry-run by default.
• I've removed the unnecessary Matrix fields.
• I've changed get_container_engine to take an Option<&str>.
• rustembedded_target no longer returns an option.
• No longer use a custom readme in Cargo.toml. lib.rs still warns about this for crates.io.

#[derive(Debug, PartialOrd, Ord, PartialEq, Eq)]
struct Image {
    repository: String,
    tag: String,
    // need to remove images by ID, not just tag
    id: String,
}

If all is good, I'll squash the commits to remove some unnecessary ones.

[Emilgardis]

Suggested change

	run: cargo install --path cross-dev --force
	run: cargo install --bin cross-dev --path . --force --features dev

[Emilgardis]

actually, this is wrong, we should just make sure to always check if it builds

[Alexhuszagh]

So remove matrix.deploy, and then just add cargo build --features=dev?

[Emilgardis]

specifying --bin cross-dev should be done too, to avoid unsync between needed features and the ci stage

[Alexhuszagh]

I think that's everything. If anything else needs to be patched, let me know, then I'll squash the commits since we have a few... extras.

I've:

• Removed the unnecessary badges.
• Squashed the commits into 3 logical commits.
• Added a build step for cross-dev which runs on every CI run.
• Inlined the documentation and removed crates_io.md.

[Emilgardis]

bors r+

[Emilgardis]

bors r-

oh yeah you wanted to squash?

[bors]

Canceled.

[Alexhuszagh]

bors r-

oh yeah you wanted to squash?

Already did.

bors r=Emilgardis

[bors]

Build succeeded:

• conclusion