add SO_PRIORITY (closes #19802)

Patch by Claudiu Popa.
asyncio: Fix get_event_loop() to call set_event_loop() when setting the loop. By Anthony Baire.
Close #19798: replace "maximum" term with "peak" in get_traced_memory()
documentation. Use also the term "current" for the current size.
Closes #19786: tracemalloc, remove the arbitrary limit of 100 frames

The limit is now 178,956,969 on 64 bit (it is greater on 32 bit because
structures are smaller).

Use int instead of Py_ssize_t to store the number of frames to have smaller
traceback_t objects.
asyncio: Change write buffer use to avoid O(N**2). Make write()/sendto() accept bytearray/memoryview too. Change some asserts with proper exceptions.
Issue #19818: tracemalloc, the number of frame limit cannot be zero anymore
Change pathlib documentation to use "raise" instead of "throw".
Encapsulate cpickle global state in a dedicated object.

This implements PEP 3121 module finalization as well. This change does not
cause any significant impact on performance.
Issue #19595: Re-enable a long-disabled test in test_winsound
Move assertFalse out to separate class.
Move assertTrue out to separate class.
Split out separate Asset super-class.
Invert sense of self.test.
Move _baseAssertEqual out to separate class.
Make msg a required keyword argument, reducing duplication.
Move assertNotEqual out to separate class.
Move assertAlmostEqual using places out to separate class.
Move assertAlmostEqual using delta out to separate class.
Move remaining assertAlmostEqual logic to separate class.
Move assertNotAlmostEqual using places out to separate class.