Zig-Zag scan

Zig-zag and inverse zig-zag scan as used in Image Processing's JPEG compression.

The functions presented within perform normal zig-zag scanning and the reverse. The normal process converts a matrix of any size into a one-dimensional array by implementing the zig-zag scan procedure.
The inverse function takes in a one-dimensional array and by specifying the desired number of rows and columns, it returns a matrix having the specified dimensions, which would yield the one-dimensional array if the normal zig-zag procedure were implemented.

Works on 2-D matrices of any dimension.