Create CLI that can convert sb3 to leopard or leopard-zip

[PullJosh]

Closes #128. Allows importing a .sb3 file and generating a leopard folder or zip directly from the CLI. I haven't implemented .sb3 output yet for the sake of time/effort. (And because .sb3 is currently the only allowed input method so it would be mostly useless.)

Example output:

I also did my best to make the errors look nice:

[towerofnix]

This is really awesome work, thank you!!

We left a bunch of comments, but they're mostly touch-ups for the code, and should be pretty quick to address. We also filed two issues following up this pull request, and did those before reviewing, to get some familiarity with the structure here. Check them out if you're curious: #130, #131

Thanks again! Apart from the code touch-ups, this looks great.

[towerofnix]

Thanks! This all looks good except for one more tweak to how asset directories are created.

[PullJosh]

@towerofnix Fixed the issue you mentioned. I also noticed that the wcwidth package was not actually counting chalk string widths correctly, so I replaced it with a "stripAnsi" function that does the job. With your approval, I think this is ready to ship.

[towerofnix]

Oops, that's a good catch (and close call) with wcwidth not doing what I thought it did! Thank you.

And thanks for addressing everything else, too, and for your work on this in general! This looks great. 🥳