New helpers and small cleanups

[freeformz]

• Additional helpers:
  • Map - maps the items in the set and returns them as a new set
  • MapTo - maps the items in the set into a provided set
  • MapToSlice - maps the items in the set and returns them as a slice
  • Filter - filters the items in the set based on the function and returns a new set
  • Reduce - reduces the items in the set to a single value
  • ReduceRight - reduces the items in the ordered set, in backwards order, to a single value
  • ForEach - calls the provided function with each member of the set
  • ForEachRight - calls the provided function for each item in the ordered set, in backwards order.
• Cleaned up some Examples so they now use New{Ordered,}With instead of New{Ordered,} and multiple Adds

#minor