Fast 2D phase unwrapping

Fast unwrapping 2D phase image using the algorithm given in:
M. A. Herraez, D. R. Burton, M. J. Lalor, and M. A. Gdeisat, "Fast two-dimensional phase-unwrapping algorithm based on sorting by reliability following a noncontinuous path", Applied Optics, Vol. 41, Issue 35, pp. 7437-7444 (2002).

Features and advantages:

* Fast algorithm (takes approx. 0.5s to unwrap 512x512 non-noisy and noisy image in my computer)
* Support ignored regions, by setting NaN to the ignored regions.

If using this code for publication, please kindly cite the following:

* M. A. Herraez, D. R. Burton, M. J. Lalor, and M. A. Gdeisat, "Fast two-dimensional phase-unwrapping algorithm based on sorting by reliability following a noncontinuous path", Applied Optics, Vol. 41, Issue 35, pp. 7437-7444 (2002).
* M. F. Kasim, "Fast 2D phase unwrapping implementation in MATLAB", https://github.com/mfkasim91/unwrap_phase/ (2017).

This algorithm is also available from GitHub (https://github.com/mfkasim91/unwrap_phase/)