`lpm x` / `lpx`

[codebycruz]

This would be useful for packages that are just command line tools, and especially nice for example code
Currently it'd be a little odd without a registry, but still useful for the example case every once in a while.

For example, this would execute the triangle example from the arisu project without you having to manually clone the repo, cd to the package, and lpm run.

lpx triangle --git https://github.com/codebycruz/arisu/tree/arisu-slang