Add optional patch output

[Miepee]

e.g. something like python -m mars_patcher input.gba output.gba patch-data.json --output-patch output.ips

[Miepee]

This needs support within the patcher to create patches. As far as I can see, we have a few options for this:

• Ship flips, offload the work to flips (very bad)
• only create IPS patches and no BPS patches and offload that work to ips.py (would work in a pinch, but ideally we'd really have bps)
• use python-bps-continued to create bps patches (very slow, discontinued, license that ideally we'd avoid)
• write our own fast functions to create bps patches, could look at flips for reference since its also gplv3.

[cluekitty]

If we wanted to write our own functions, I have a saved copy of the BPS spec from byuu.org before it went offline

[biosp4rk]

I don't mind recreating flips code for creating patches in python

[duncathan]

what's the point of doing this instead of just patching the game?