Add metadata commands

[SwagColoredKitteh]

Add metadata using a #META command, which sets various preferred attributes that can be overridden with CLI parameters.

• [ ] #META DELAY <FRAME DELAY> for setting the frame delay
• [ ] #META CANVAS_SIZE <W>x<H> for setting a preferred canvas size
• [ ] #META TOTAL_FRAME_COUNT <COUNT> for setting a total frame count, this would help with the progress bar while the data is getting loaded

Not sure whether to only allow #META at the start of the file. Changing the metadata while playing seems like a good idea for things like TOTAL_FRAME_COUNT so that whatever is feeding data can adaptively adjust that.

[MarcosCosmos]

This would definitely be a good feature for configuring to match the turn delays of different games for example (it would be important for using it on the fly supposing we do PVC)

[SwagColoredKitteh]

Would be nice to have one for the background color, too!