New "fit" option for asciinema-player, maximize controls area

[relikd]

Hello, I just published a macOS Quicklook plugin for .cast files.
https://github.com/relikd/QLAsciicast

Currently I use fit: "both" which uses most of the available space (while keeping aspect ratio). However, I would prefer if there was a mode which maximizes the player overlay area to fill all available space. The recording inside should still only fit to the shorter side, but the controls could be larger than that.

The "both" option is okay, but it would look better if the controls would fill the whole preview area.