add #or_else
add #each
Add #map and #flat_map
refactor #each and #map to use #flat_map
Automatically rescue exceptions in #flat_map, and propagate rescue list
Extend automatic rescuing to #map
Restore exception raising in #each, matching Scala's Try.foreach
add #select and (#find_all alias)
Add #transform
Oops, forgot #select and #find_all for Failure