Added definitions for new operators in 'instructions' file.
Implemented 'chained' relational operators.  Ex: a < b <= c = d.

- Added 'the_T_sym' for true value.  This is a global constant created in
  init_values().  (values.c)
- Added instructions: I_DUP_ROLL_3, I_DUP, I_SWAP.
  (instructions, vm.c + generated files)