index or subscript in datatip

A datatip text update function that displays linear index or subscript information within the datatip (see figure with the additional "@..." lines).
Simple, but helpful e.g. if you want to find out index ranges of interest of your plotted data.

(note: the code was created without influence by http://www.mathworks.com/matlabcentral/fileexchange/11212-moreindatatip which has similar functionality)