collections template functions

[technosophos]

Per #25, implement the Sprig functions for Bartholomew. Rather than file an issue for each function, I figured I'd break these down into small batches. (Note: I am not entirely sure all of the functions can be done with the same syntax. I am no pro in writing the Handlebars functions.)

• list A B C returns a list of [A, B, C]
• first LIST returns the first item in a list
• rest LIST returns all but the first in a list
• last LIST returns the last item in a list
• initial LIST returns all but the last in a list
• append ITEM LIST appends an item to end of a list (not sure if this one makes sense to add)
• prepend ITEM LIST appends an item to start of a list (not sure if this one makes sense to add)
• concat LIST LIST concatenate two lists into one list
• reverse LIST reverse the order if items in a list
• uniq LIST remove duplicates form a list. uniq [1, 1, 1, 2, 2] produces [1, 2]
• without ITEM LIST removes ITEM from the list
• has ITEM LIST returns boolean true of the item is in the list
• compact LIST removes empty items from a list (I think rhai has a definition of empty that we could use here)
• slice START END LIST extract START-END from a list and return it
• chunk SIZE LIST chunk a given list into a list of lists, each no larger than SIZE