Switch the RTL characters array to a ranges array (#8)
Switch the RTL characters array to a ranges array (#8)

Not having the complete array in the source but instead, just the
possible ranges has a size saving of about 15Kb.
In addition, usage was change to a function called 'isStrongRTLChar'
which makes the code clearer and more readable.
gkatsev/vtt.js,gkatsev/vtt.js