add arrays of functions to spec

[ansis]

These properties need to support functions. I'm not sure how arrays for functions should be specified in the spec.

• {fill,line,text,icon}-translate
• line-dasharray
• raster-brightness

[lbud]

I've been working on getting the validate script to pass and this validates fine, but does it make sense/look alright in the spec?:

    "line-dasharray": {
      "type": "array",
      "value": ["number", "function"],
      "length": 2,
      "default": [
        1,
        -1
      ],
      "function": true,
      "transition": true
    },

whereas before it had "value": "number",

Is it fine for value to support an array of possible values, or does that break things elsewhere?
(The other option I had been playing with was adding an option in fn for an array of functions, but I hadn't gotten that to work and it also seems too specific a case to allow any fn definition to accept an array of fns)

[kkaefer]

They already support functions on native.

[jfirebaugh]

Add in #86.