2x2, 3x3 and Nxn Space-Filling Curves

Implementation of all possible forms of 2x2 and 3x3 space-filling curves, i.e., the generalized forms of the Hilbert curve < https://en.wikipedia.org/wiki/Hilbert_curve>, the Peano curve < https://en.wikipedia.org/wiki/Peano_curve> and the Peano curve in the meander type (Figure 5 in < https://eudml.org/doc/141086>). It can generates nxn curves expanded from any specific level-1 units. It also implements the H-curve and the three-dimensional Hilbert curve. See for more details.