building dlib as a shared library.

build to use fftw.

the quality of a track association function.

to move to a new position but was random amongst all permutations with such
moves.  However, this isn't really fully random so this function has been fixed
so it does exactly what the spec says it should.

to remember, or even understand, that they should add it themselves.  However,
this change breaks backwards compatibility with the previous serialization
format for assignment_function objects.

they are updated at least once with a detection.

tools.  So this adds the track_association_function and structural_track_association_trainer
objects and also test_track_association_function() and cross_validate_track_association_trainer()
routines.