Add [cycle] tag to allow for cycling between different custom colours

[JujuAdams]

The [rainbow] effect cycles the blend colour of a specific portion of text through the entire hue-space.

Sometimes, however, it's useful to cycle through a specific selection of colours. The [cycle] tag should take a variable number of arguments (up to some maximum e.g. 8) and then pass this data to the shader. Each argument is a value from 0 - 255 and describes a hue. The shader then cycles between these hues by interpolating through RGB space.

[JujuAdams]

...could also interpolate through YUV space?

[DragoniteSpam]

I foresee using this to make text of the default color flash to red or blue or something periodically. This should be interesting.

[JujuAdams]

Implemented for v6.0.8