Modularization

Implementing steps 3 and 4 from issue #17.
As a result of this modularization (in particularly the breakout of the content edge,
as well as the implementation of stripe-skipping and positional independence modules so
that normal and relaxed schemas could be created), 
the verification by instance generation became feasible (issue #23).

The errors generated from the instance generation procedure uncovered several errors in the RNC,
(issue #34) which have all been fixed.

The content models (from Jing -s) have been updated (issue #16).

close #34