unwrap: Split input normalization to separate function.
Add a function to find residues for phase unwrapping.
unwrap: Expand test for find_phase_residues.
unwrap: Add example to find_phase_residues docstring.
unwrap: More intuitive variable naming.
unwrap: Clean up cython code.
unwrap: Rename cython func find_phase_residues_cy
unwrap: Use masked arrays in handling residues when wrap_around=False.
unwrap: Use print_function in cython.
unwrap: Implemented setup for branch cuts.
unwrap: Implemented branch cuts.

Tests for small images with wrap around and no masked entries seems
promising. The branch cut core should be ready for masked images and
image borders, but this has not yet been implemented in the setup logic
that defines the problem.

Included with these changes are a queue implementation in C
(the files queue.{c,h}) which is part of the c-algorithms library,
copyright Simon Howard and released under the BSD-like ISC license.