VT525 colour improvements

[davidrg]

Finish off as much of VT525 colour support as possible, and with it the Colour Text Extension

• Add new VT525 colour palettes and fix operation of DECSTGLT.
• Implement DECECM
• Fix cursor colour when using the VT525 palette, and any other screen elements that are using inappropriate palette colours
• Implement the DEC Alternate Colour Mode colour attribute quirk
• Implement DECCTR
• Add extension 22 to the DA response for the K95 terminal type

I think for now I'll leave off a command to let users view and customise the Alternate Colour Mode attribute colours as it seems unlikely to be used.

[j4james]

I've got a little test script demonstrating the effects of DECECM which you can use to double check your implementation: https://gist.github.com/j4james/cac2cec7fe0df78e59eb52f9c8201599

VT525 screenshot showing DECECM set

VT525 screenshot showing DECECM reset

[davidrg]

Thanks for that! I'll give it a go this evening, though I suspect the lack of left/right margin support in K95 may present some issues. That's next on my list after finishing off colour support though!

[davidrg]

I hope this if not correct than at least more correct than it was before! RGB colours are now converted to the nearest shade of grey in the mono palette when in that mode:

And using SGR while in Alternate Colour mode results in the alternate colour indicies being applied, while text output before use of SGR is unaffected by being in Alternate Colour mode:

[davidrg]

One side of DECCTR done!