Natural, Integer, and Rational numbers
- added Value() methods to access small Natural and Integers
  as uint64 or int64 respectively, and to get the components
  of Rational numbers
- fixed a bug with Integer creation
- removed some _'s from names
- added more comments in places
- added test cases

R=rsc
DELTA=184  (127 added, 11 deleted, 46 changed)
OCL=31210
CL=31265