Resolve #48 - Create and test new IdentityParser type

The identity parser is a parser for the identities of a specific entity type,
and it may be constructed using a static factory method.  This method scans the
inheritance hierarchy of the target entity in order to create an appropriate
instance.

* Rewrite old/obsolete functionality to use the new IdentityParser.

* Provide convenience methods for quick parsing.

* Update unit tests.

* Create new unit tests for new functionality.
Trivial change to a comment, relating to the creation of issue #63