Update Subproject
format: Adds TagxTag class and generation method
format: Adds VariableWidthInteger and NcxRecord
index: Adds IndexReader and Aggregate record
enumerations: Adds Enumerations

Mostly a direct port of the old version, with slight modifications for
generic parsing.
Pdb/MobiFile: structural changes

This patch splits some language fields into two shorts for dialect and
base language, adds index reading to the MobiFile parse routine and
changes some package private modifiers to public for ease of development
since these classes will ultimately become implementation details of a
more abstract model in later versions.

Last, we update the Inspect and Unpack utilities for the new
structure and add enumeration parsing to the output.