Add unit tests related to #11 - the serializer factory
Resolve #7 - Add new 'TryParse'-style API for parsing and rendering values

This new API introduces two new methods to mapping helpers:
* Parse
* Render

These new methods use a function that has similar signature to the 'TryParse'
methods built into many framework types.  These methods return a boolean and
expose their output via an 'out' parameter.

This new functionality is now built into the models as well as the mapping
helpers for the parser.  The parsing/rendering functions themselves are
represented by three new delegates.

Backwards compatibility at this stage is preserved by setting the new
parsing/rendering functions from the old property setters.
Resolve #17 - Mark tests which test the public API as such.
Resolve #16 - Remove unneeded interfaces and fix unit tests

This commit removes a number of unneeded interfaces from the codebase, which
were not adding any value.  Also, as a result, a number of unit tests needed to
be altered and fixed.