This commit does quite a few things in order to get this to work:
1. We move all of the code dealing with knowing which command to run
into it's own function. This wrapper command allows us to always
close out PBAR before dumping error output. This fixes a problem
where stderr and stdout were borked and not printing out error
messages correctly.
2. We then refactor the code that has a panic to return early with that
error message.
3. If the command we ran errored, we print out with PBAR that there was
an error with the program we ran (not wasm-pack itself) then dump the
stderr from the command to the actual stderr
This means we can abort early on without continuing any of the other
parts of wasm-pack and let the user know what the error was rather than
just saying "There's an error"
Michael Gattozzi