change API code to reflect Grape preferences
change API code to reflect Grape preferences

These changes made in effort to reuse existing code but also reflecting
limits of that approach with how Grape wants to validate parameters.
* ‘/:endpoint’ has to be changed, the mixed approach of validating
String or DateTime not tenable.
* there is now a single endpoint for a single time parameter and a very
broad function that evaluates a from and to value using the
DateWrangler class

theodi/bothan,theodi/bothan,theodi/metrics-api,theodi/bothan,theodi/bothan,theodi/metrics-api,theodi/metrics-api