Support other cargo wrappers with bevy build/run

[TimJentzsch]

Can this run another binary than cargo? On Windows, you need to run cargo-clif in order to use cranelift.

Originally posted by @janhohenheim in #24 (comment)

[janhohenheim]

Also important for cargo-mommy, of course ~

[BD103]

I feel like environmental variables best fit this use-case. Maybe something like BEVY_CLI_CARGO=/path/to/cargo?

[janhohenheim]

While we are on it, we could also specify another path for rustup. I don't know any use-case for that though.

[BD103]

While we are on it, we could also specify another path for rustup. I don't know any use-case for that though.

This could be useful if:

1. You're a rustup developer and have multiple instance installed.
2. You installed rustup in a custom way, making it not always on the PATH.

I would like all of these environmental variables documented, though. Perhaps through bevy --help or a man page?

[janhohenheim]

Update for others reading this: Tim already implemented the rustup env var as BEVY_CLI_RUSTUP :)