Generates free pathname for a file

Generates pathname to a non-existing file so you can save data without overwriting an existing file.

Usage : filename = genfilename(fname)
This simple code will generate a 'free' pathname based on your suggestion (fname), to make sure you can save your data to a file without overwriting to an existing one.

Simple options allow you to use a certain number of digits or start numbering at a defined number.