===============================================
KerningPair - class to represent kerning pair
===============================================
This class is Multiple Master - compatible
CONSTRUCTOR:
KerningPair() - generic constructor, creates an empty KerningPair
KerningPair(KerningPair) - copy constructor
KerningPair(index) - creates a KerningPair to glyph referenced by index but zero value
KerningPair(index, value) - creates a KerningPair to glyph referenced by index but and assigns value
ATTRIBUTES:
parent (read-only) - KerningPair's parent object, Glyph
key (integer) - index of right glyph of the pair
value (integer) - value of the pair
values [(integer)] - list of values for each master
OPERATIONS:
METHODS