Add cargo-style output diagnostics.

[Alexhuszagh]

Adds the quiet and color command-line flags, where color supports auto, always, and never`. These command-line flags are parsed to a verbosity which can be quiet, normal, or verbose.

With these, we then have the stderr message formatters:

• fatal_usage: print a fatal error message with the failing argument, and add a help context menu for how to use cross.
• fatal: print red 'error' message and exit with an error code
• error: print red 'error' message
• warn: print amber 'warning' message
• note: print cyan 'note' message
• status: print an uncolored and unprefixed 'status' message

We have the stdout message formatters:

• print: always print the message
• info: print the message as long as the verbosity is not quiet
• debug: only print the message if the output is not quiet

We also have a few specialized error handlers, and methods to help ensure we can have flexible error reporting in the future:

• status_stderr
• status_stdout

The command extensions now have, print, info, and debug, which formats the command and sends it to the shell. This allows us to avoid using print_verbose where we sometimes manually override the default setting.

A few of these settings aren't currently used (such as info and status, but they're a very common pattern), so we can ensure we have the necessary utilities to ensure we can properly format messages in the future. A few like shell::print are practically identical to println!, but this allows us to customize it if need be in the future.

Solves parts of #797.

[Alexhuszagh]

We only manually intercept --color if it's invalid, or --verbose and --quiet if both are set, and let everything else be handled by cargo. Some sample differences (where target/debug/cross is my local branch, and cross is the v0.2.2 release) are:

There's quite a dramatic difference.

For a few things, like Github Actions, to ensure we don't remove the println!/panic! statements, I've moved them all to xtask/util and labeled them as follows:

• gha_print
• gha_error
• gha_output

I've also updated it so in quiet mode it silences rustup.

[Emilgardis]

Awesome, looks great

I don't think this solves #797 however, but it's a good way to it

bors r+

[bors]

Build failed:

• conclusion

[Emilgardis]

bors r+

[bors]

Build succeeded:

• conclusion