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