compute tversky index

compute.tversky( a, b[, opts] )

Computes the Tversky Index between two sequences.

var a = 'beep',
	b = 'boop';

var idx = compute.tversky( a, b );

var c = [ 4, 2, 3, 5, 7 ],
	d = [ 2, 4, 3, 1 ];

var idx = compute.tversky( c, d );