Enable coloured tablature symbols

[reinierdevalk]

As seen in, e.g., the Capirola MS and some of the vihuela books.

Examples:
capirola-no_1.png

fuenllana-1554_3-no_31.png

[DILewis]

I think we're ok for notes, because they're already able to take @color. We just need to remember to do the same for rhythm flags. There are rules for Capirola, but implementing those seems like overkill, given that it's unique for that.

[reinierdevalk]

@DILewis Yes - then this issue can serve as that reminder. I'm just adding everything I can think of.