* Correct the behaviour of parsing `rgb:R/G/B`. It should be interpreted
as `RR/GG/BB` instead of `0R/0G/0B`
* Add support for `rgb:RRR/GGG/BBB` and `rgb:RRRR/GGGG/BBBB`. The
behaviour of 12 bit variants is to repeat the first digit at the end,
e.g. `rgb:123/456/789` becomes `rgb:1231/4564/7897`.
* Add support for `#` formats. We are following the rules of
[XParseColor] by interpreting `#RGB` as `R000G000B000`.
* Add support for XOrg app color names, which are supported by xterm, VTE
and many other terminal emulators.
* Multi-parameter OSC 4 is now supported.
* The chaining of OSC 10-12 is not yet supported. But the parameter
validation is relaxed by parsing the parameters as multi-params but
only use the first one, which means `\e]10;rgb:R/G/B;` and
`\e]10:rgb:R/G/B;invalid` will execute `OSC 10` with the first color
correctly. This fixes some of the issues mentioned in #942 but not
all of them.
[XParseColor]: https://linux.die.net/man/3/xparsecolorCloses#3715