back FmtStr objects with Blessed/Blessings colorstring output

[thomasballinger]

We could do this before we switch to Blessed, but it'd be large.

[thomasballinger]

The weakest version of this would be just ripping out termformatconstants.py, but there's a lot of other duplicated work too.

Another option would be completely doing away with our own internal representation, and reparsing terminal-formatted strings each time we do math with them.

FmtStrs are nice for doing things like "start with a line, then stick the text "hello" in bold into spaces 10-16 of it. I'm not sure how this works with the fact that YOU DON'T ACTUALLY KNOW how big a string is until you're talking about a specific terminal (double width characters). Cutting into it is going to be more complicated.

[thomasballinger]

This sounds harder and less important than fixing the input code.

[thomasballinger]

Most important is giving parsing input character sequences and understanding them via blessed - let's start with that

[thomasballinger]

blocked on Blessed getting better parsing so that code can be used to produce FmtStrs