Add support for resolving artifacts with DateTime versions

[mmsmits]

The package library now sometimes parses version values of Conformance resources as SemVer, however, these elements can also contain other version algorithms like date/time, alphabetic etc see:

http://hl7.org/fhir/structuredefinition-definitions.html#StructureDefinition.versionAlgorithm_x_

For now, make sure we also use a date/time algorithms to resolve the best candidate when encountering multiple versions of an algorithm in the resolver.