added new Example, which illustrates the use of the PartiallyFixedModelBuider to enforce that a fitting result matches the given landmark points.
Introduced Posterior Model Builder, which replaces the PartiallyFixedModelBuilder.

We have refactored the PartiallyFixedModelBuilder such that the code closely corresponds to the theory and notation used in our Media paper "Posterior Shape Models". To make the connection more clear, we have saved it under the new name PosteriorModelBuilder. The PartiallyFixedModelBuilder is deprecated and will in future versions be removed.
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.
Works with (sigma2 * Id) set in the method as point covariance.
Tests now work for PosteriorModelBuilder using sigma2I as a covariance
matrix, set in a dedicated C++ method.
Now has a C++ test that sets a uniform matrix from the outside.
Removed the bug that the covariance and precision matrix were confused.
The C++ test now has a simple test with a one-point model, but
non-uniform point covariance matrix. Seems to be working.
Posterior model builder now has a test that acutally tests the 3D
posterior with an anisotropic noise model for one point.
Added ITK posterior model builder.
Changed test posterior model builder C++ test to use eigen functionality
rather than VTK for finding tangential vectors.
Merge pull request #17 from marcelluethi/landmark-constrained-fitting-example

Added new Example for fitting a landmark constrained model
Merge pull request #18 from marcelluethi/release-0.81

Preparations for an intermediate release 0.81
added a more general application for building vtkPolyData shape models
Merge branch 'marcelluethi-posterior_model_builder' into main_master
Merge pull request #19 from marcelluethi/posterior_model_builder

Introduced Posterior Model Builder, which replaces the PartiallyFixedModelBuilder
Merge branch 'master' of https://github.com/statismo/statismo into main_master
added method PointToVector to representer interface
Added GaussianProcess registration functionality.
change refLandmarks to modelLandmark in assert
Made use of std::async optionally

The feature, which is not supported by all compilers, needs to be
explicitly enabled with CMake.