Integrated additional MI work on a Tcl_ObjType for lazier construction
of the Tcl strcutures from the json C structures.

Notes
- Modified the Tcl parser to return 0|1 for boolean values, to match
  the new C parser. Updated testsuite.
- Supplied my own definition of assert to fit in with Tcl (Tcl_Panic).
- Modified the C conversion of json null to match the Tcl parser, is
  now 'null', not the empty string.
- Changed Tcl_Dict* uses to equivalent Tcl_List* to keep the code
  usable for Tcl 8.4
- Moved the code handling the deferal/laziness into lazy_value2obj and
  applied it to array elements as well, not just object fields.
- Moved the variables in value2obj into the switch branches.
- Changed the Tcl_ObjType structure initialization to regular C.
  Code as provided (see ticket attachment json2.c) looked like some
  GCC-ism.

Open question
- Why does the json2string function not just generate the string rep,
  but takes the int.rep as well, shimmering the Tcl_Obj*. Seems to
  presume that the string generation is immediately followed by Tcl
  code forcing a shimmer anyway ?!

Reduced testsuite passes.