Commented out freitag smoothing.

Freitag smoothing could lead to degenerate triangles and it did not
seem to improve quality significantly.
Split the klincsek_triangulation function in two.
Klincsek triangulation clean up.
Added get_edge and get_face functions.
Added flip_32, flip_23 and flip_44 functions.
Changed the min_quality(edge) function.
Changed the edge removal implementation radically.

It now follows the article by Shewchuk: Two Discrete Optimization
Algorithms for the Topological Improvement of Tetrahedral Meshes.
2-3 flip and 3-2 flip working.

Splits and collapses should be replaced by more efficient reconnection
operations.
Removed debug info.