Fix some incorrect SGR codes

[TBBle]

I came across this as a suggested test suite for Windows Terminal, and while trying it out, I hit a few issues:

• The 'Rapid blink' line continued blinking in the no-blink section
• The SGR 38 and 48 colour parameters incorrectly implemented the ITU T.416-conformant layout.

Windows Terminal doesn't currently implement the latter, but there was a fair bit of research done on https://github.com/microsoft/terminal/issues/4321 as preparation work. Per https://gist.github.com/XVilka/8346728#gistcomment-2774523 there is some ambiguity in the specification, so for the purposes of this repo, it might make sense to make that change toggleable as well?