co_lnotab supports negative line number delta

Issue #26107: The format of the co_lnotab attribute of code objects changes to
support negative line number delta.

Changes:

* assemble_lnotab(): if line number delta is less than -128 or greater than
  127, emit multiple (offset_delta, lineno_delta) in co_lnotab
* update functions decoding co_lnotab to use signed 8-bit integers

  - dis.findlinestarts()
  - PyCode_Addr2Line()
  - _PyCode_CheckLineNumber()
  - frame_setlineno()

* update lnotab_notes.txt
* increase importlib MAGIC_NUMBER to 3361
* document the change in What's New in Python 3.6
* cleanup also PyCode_Optimize() to use better variable names

Include/code.h

@@ -117,7 +117,7 @@ PyAPI_FUNC(int) _PyCode_CheckLineNumber(PyCodeObject* co,
 #endif
 
 PyAPI_FUNC(PyObject*) PyCode_Optimize(PyObject *code, PyObject* consts,
-                                      PyObject *names, PyObject *lineno_obj);
+                                      PyObject *names, PyObject *lnotab);
 
 #ifdef __cplusplus
 }