Add build entries that run rustc similar to the default package.

[marcospb19]

I'm learning Rust, and was using the sublime's default Rust package, it allows me to run rustc and then, run the executable, here's the command.

"shell_cmd": "rustc \"$file\" && \"./$file_base_name\"",

After installing Rust Enhanced, I'm unable to run like this.

I can make a little hack here editing the .build file, but my proposal is to add the equivalent command to this package.

[ehuss]

I believe it is not entirely trivial, because the build system uses its own build logic, and it doesn't know anything about shell_cmd. That could be added, of course. Also, FYI, the "Script" variant is intended for this use case, but requires installing cargo-script.