Feature: Create mapping provider interface and handling code

[dclucas]

A user should be able to provide custom mapping for a given Source/Target combination by implementing a simple interface:

public class PersonPersonEditModelMappingProvider : MappingProvider<Person, PersonEditModel>
{
      public void AddMappings()
      {
            this.AddMapping()
               .From(s => s.Name + s.LastName)
               .To(t => t.FullName)
      }
}

The design needs to either have a base class that provides an AddMapping method or to provide an interface that receives a repo (or a new MappingAdder class or such) and uses it. While the interface is more easily testable, the base class enforces a segregation by source/target more easily.

[dclucas]

Implemented in version 0.9