shadow gradient and rainbow tags

[zml2008]

Done as a quick tech demo, would need a bit of actual design work and cleanup if we want to actually incorporate this into MM

<gradow:red:blue>hello world

<shainbow>what kind of day is <aqua>this?

[Andre601]

Personal opinion, but I feel like shadient would be a better name than gradow. Tho, that's more a personal preference (maybe allow it as an alias?).

[oliviathevampire]

What would this look like with a normal gradient and a shadow gradient?