Feature: Create base mapper class, for custom mapping extension

[dclucas]

Keep BaseMapper for coders who are expanding the library, but provide developers a way to inherit mapping functionality and specialize it through code.

As in:

public class CustomerMVMMapper : Mapper<Customer, CustomerMVVM)
{
    public CustomerMVMMapper()
    {
        // this guy should inherit from composite mapper and upon this constructor call already have all the mapper stack ready.
        AddMapping( /* magic mapping here */);
    }
}

[dclucas]

Closing in favor of a better approach.