Generate all the opcodes in a pickle.
'pickle' is a file-like object, or string, containing the pickle.
Each opcode in the pickle is generated, from the current pickle position,
stopping after a STOP opcode is delivered. A triple is generated for
each opcode:
opcode, arg, pos
opcode is an OpcodeInfo record, describing the current opcode.
If the opcode has an argument embedded in the pickle, arg is its decoded
value, as a Python object. If the opcode doesn't have an argument, arg
is None.
If the pickle has a tell() method, pos was the value of pickle.tell()
before reading the current opcode. If the pickle is a bytes object,
it's wrapped in a BytesIO object, and the latter's tell() result is
used. Else (the pickle doesn't have a tell(), and it's not obvious how
to query its current position) pos is None.