Add :cargo command

[sigmaSd]

Currently we have a lot of commands like :expand :asm that just wraps cargo plugins, I don't think its realistic to support all cargo plugins.

The user currently can use irust scripts for unimplemented commands but that seems to much work.

I propose adding :cargo $args command that just invokes cargo inside irust repl directory and forwards the user argument to it.
I think it should make things a lot better.

One implementation note, parsing user arguments should take in consideration arguments in quotes like :cargo plugin "quoted arg" arg2

[actuday6418]

Maybe there could be a general way to execute any shell command from within irust instead, always run inside the repl crate directory. Something like :sh cargo $args.

[sigmaSd]

There is already ! to execute shell commands, I guess your idea is more general and makes sense

the prefix should maybe be !! or like the one you proposed