Add support for inverse colour escape code.

[emmalexandria]

I might be using this wrong somehow, but when I run a program that uses inverse text colors (switches text and background colors) it isn't captured in the screenshot.

[HeavyWombat]

Thanks for bringing it up. I assume this is about the SGR parameter code 7:

Reverse video or invert | Swap foreground and background colors; inconsistent emulation

This is not implemented yet in the custom parser that is used in termshot. I put that on my list of things to add to the tool. It is one of those features that I rarely or never use and therefore did not include.