Toy project; cash register change calculator in different languages

Ruby source, running under JRuby as well, is the original version, tested, commented and handling I/O. ruby Ruby/main.rb runs the REPL that supports the commands written in the original spec (help can help), rspec Ruby/test/rb runs the test suite.

Scala source is an almost line-for-line port of the Ruby version. The only Scala-specific feature is use of Options for the recursive change calculator. sbt test in Scala directory runs the test suite.

Many forms of malformed input are not caught correctly and would provide uncaught exceptions in both implementations. This remains to be fixed.