New data formats

• The sparse matrix=(cols,rows) option to plot and splot generates a uniform pixel grid into which individual pixel values may be loaded in any order. This is useful for plotting heat maps from incomplete data. See sparse.
• During input of non-uniform matrix data, column(0) now returns the linear ordering of matrix elements. I.e. for element A[i,j] in an MxN matrix A, column(0)/M gives the row index i, and column(0)%M gives the column index j.