view.obj==NULL and view.obj==base.

if the view has exported buffers. Make this official by uncommenting
a test case.

Issue #14007: accept incomplete TreeBuilder objects (missing start/end/data/close) for the Python implementation as well. Add disabled tests for the doctype() method.

getbuffer redirection scheme.

Patch by Zooko O'Whielacronx.

Issue #14166: Pickler objects now have an optional `dispatch_table` attribute which allows to set custom per-pickler reduction functions.
Patch by sbt.

This makes the C implementation more aligned with the Python implementation.
Also added some tests to ensure that Element is now a type and that it can
be subclassed.

Add checks in PyUnicode_WriteChar() and convert PyUnicode_New() assertion to a
test raising a Python exception.