Add support for linear time morphological operator (for Toggle Mapping with large structuring element)

[DoubangoTelecom]

https://pdfs.semanticscholar.org/80d8/786efc0ac6f578bc8b9b057ee3822deea0d0.pdf
http://tpgit.github.io/UnOfficialLeptDocs/leptonica/grayscale-morphology.html