Restructured XSD file:
- Ordered elements to follow IDF Format Specification Document more closely.
- Removed max and min occurrences from elements, since these cannot be
  checked efficiently while not requiring order.  (Number of occurrences
  will be checked in the Java code.)
- Made all changes needed to conform with IDF Format Specification as
  pointed out by Oladapo's analysis of March 2013.