added new Example, which illustrates the use of the PartiallyFixedModelBuider to enforce that a fitting result matches the given landmark points.
Moved initialization of constants out of class definition.

Defining constants of type double directly in the class declaration seems to be disallowed in Visual Studio.
Merge pull request #17 from marcelluethi/landmark-constrained-fitting-example

Added new Example for fitting a landmark constrained model