Each subtable has a number of instance variables.
kern
A two level hash array containing kerning values. The indexing is left
value and then right value. In the case of type 2 tables, the indexing
is via left class and right class. It may seem using hashes is strange,
but most tables are not type 2 and this method saves empty array values.
type
Stores the table type. Only type 0 and type 2 tables are specified for
TrueType so far.
coverage
A bit field of coverage information regarding the kerning value. See the
TrueType specification for details.
Version
Contains the version number of the table.
Num
Number of kerning pairs in this type 0 table.
left
An array indexed by glyph  left_first which returns a class number for
the glyph in type 2 tables.
right
An array indexed by glyph  right_first which returns a class number for
the glyph in type 2 tables.
left_first
the glyph number of the first element in the left array for type 2 tables.
right_first
the glyph number of the first element in the right array for type 2 tables.
num_left
Number of left classes
num_right
Number of right classes
