Add a check before clipping the data to the actual_range specified in the netCDF file so as to only perform the clipping when the actual_range has been specified
Pretty comprehensive overhaul of the code to:

    1) Make it faster
    2) Make it more readable

The loops over each line of the file (after the initial reading to find
the number of vertices (nodes), elements, header lines, node strings
etc.) have been replaced with much quicker textscans of the appropriate
number of lines. In addition to other improvements (using strcmpi
instead of using ==, for example), the overall runtime for a 250,000
node grid has been more than halved (from ~70 seconds to ~30 seconds).