Load parts of a data file

Function allowing loading of every n'th row and arbitrary columns of named file.

Essentially a wrapper for textscan, but requiring less everyday coding. Just tell the function the file, whether you want all rows or every n'th, which (or all) columns you want, and the maximum number of rows to load (if you don't know how big the file is).

The script assumes that an individual line in the file is of a manageable size, and that all lines have the same length.