CPython bytecode changes

There have been several major changes to the :term:`bytecode` in Python 3.6.

* The Python interpreter now uses a 16-bit wordcode instead of bytecode.

(Contributed by Demur Rumed with input and reviews from

Serhiy Storchaka and Victor Stinner in :issue:`26647` and :issue:`28050`.)

* The new :opcode:`FORMAT_VALUE` and :opcode:`BUILD_STRING` opcodes as part

of the :ref:`formatted string literal <whatsnew36-pep498>` implementation.

(Contributed by Eric Smith in :issue:`25483` and

Serhiy Storchaka in :issue:`27078`.)

* The new :opcode:`BUILD_CONST_KEY_MAP` opcode to optimize the creation

of dictionaries with constant keys.

(Contributed by Serhiy Storchaka in :issue:`27140`.)

* The function call opcodes have been heavily reworked for better performance

and simpler implementation.

The :opcode:`MAKE_FUNCTION`, :opcode:`CALL_FUNCTION`,

:opcode:`CALL_FUNCTION_KW` and :opcode:`BUILD_MAP_UNPACK_WITH_CALL` opcodes

have been modified, the new :opcode:`CALL_FUNCTION_EX` and

:opcode:`BUILD_TUPLE_UNPACK_WITH_CALL` have been added, and

``CALL_FUNCTION_VAR``, ``CALL_FUNCTION_VAR_KW`` and ``MAKE_CLOSURE`` opcodes

have been removed.

(Contributed by Demur Rumed in :issue:`27095`, and Serhiy Storchaka in

:issue:`27213`, :issue:`28257`.)

* The new :opcode:`SETUP_ANNOTATIONS` and :opcode:`STORE_ANNOTATION` opcodes

have been added to support the new :term:`variable annotation` syntax.

(Contributed by Ivan Levkivskyi in :issue:`27985`.)