Initial steps in switching to new contain key/value syntax that uses Key/ValueMappings.
Next step in migrating to new contain key/value approach.
Got rid of newKey and newValue in tests, so now old tests are running new key/value approach.
Dropped oldKey and oldValue stuff, and the implicit conversions for MapShouldWrapper
and JavaMapShouldWrapper, plus the implicit that converted a Map Matcher to a JavaMap Matcher.
Commented out private things that are just being stored for later.
Added missing tests for matcher and/or contain key/value, and functionality.