ListAdd
Can convert ruby numbers to Numbers
ConvertFromRubyChar and ConvertFromRubyString
Remove play.rb

Since it doesn't contain anything not in ruby_interop anymore.
ListReverse
Associative lists with numbers as keys

Wound up building "list find" while on this, probbaly extract it when convenient.
Associative lists with strings as keys

Extract some string helpers (StringsEqual, AssertStringsEqual)