Collection type: field map

--Overview--

A 'field map' is a [[type:map]], but indexed by [[type:field]]s.

For instance if a game specifies the fields:
>field:
>	type: text
>	name: field1
>field:
>	type: color
>	name: field2

Then the a field map of ''things'' for those fields would look like:
>field1: thing
>field2: thing

A field map of [[type:style]]s would be:
>field1: # some text style for field1 goes here
>field2: # some color style for field2 goes here

And a field map of [[type:value]]s would be:
>field1: text goes here
>field2: rgb(1,2,3)

--Script syntax--

In a script field maps can be accessed like normal [[type:map]]s based on the field name.
So:
>card.field1 # retrieve the value of field1
>card["field" + 1] # the same thing
>card_style.field2 # retrieve the styling for field2
