1.0.21: threshold: add Fox and Window

[zvezdochiot]

Threshold "Fox" (== "Wolf" + Singh memory optimization):

 * \brief Image binarization using Fox's local thresholding method.
 *
 * Modification of the Wolf threshold using the Singh optimization
 * of the Sauvola threshold.
 *
 * C. Wolf, J.M. Jolion, F. Chassaing. "Text localization, enhancement and
 * binarization in multimedia documents."
 * http://liris.cnrs.fr/christian.wolf/papers/icpr2002v.pdf
 *
 * Singh, O. I., Sinam, T., James, O., & Singh, T. R. (2012).
 * Local contrast and mean based thresholding technique in image binarization.
 * International Journal of Computer Applications, 51, 5-10.
 * https://research.ijcaonline.org/volume51/number6/pxc3881362.pdf

Threshold "Window":

 * \brief Image binarization using Dynamic Window based thresholding method.
 *
 * Bataineh, B., Abdullah, S. N. H. S., & Omar, K. (2011).
 * An adaptive local binarization method for document images based
 * on a novel thresholding method and  dynamic windows.
 * Pattern Recognition Letters, 32(14), 1805–1813.