- No more 0L or similar.

- Added cross-refs to fraction & decimal in numeric types.
- Moved str.isdecimal() & str.isnumeric() into alphabetical order like
  all the other str methods; also massaged the text a bit to make it
  more consistent with the similar methods' texts.

BTW The iterator.__iter__() docs seems to be out of step with
functions.rst (where it now has an extra parameter).