nghttp2: update to 1.43

nghttp2: update to 1.43

3dc6c0af Bump version number to 1.43.0
e8762781 Update AUTHORS
2bf841e2 workflow: Build with UBSAN enabled
7ebab98e Merge pull request #1548 from nghttp2/py3-bindings
23fc6cc9 Bump Linux runner OS to ubuntu 20.04
2e35cdea Update doc
22af8e78 Require python3 for python bindings
c88e9100 Update ax_python_devel.m4
43ba3125 Merge pull request #1547 from nghttp2/sphinx-v3.3
3c17299a Update enum references
a7ecff65 Make doc generation work with sphinx v3.3
79a4f789 Merge pull request #1546 from nghttp2/py3-scripts
28ba0b37 Update document reference
6b7ade9f Require python3 for python scripts
46536729 Bump clang-format to 10
563c1173 Merge pull request #1544 from nghttp2/nghttpx-clear-mcpool
1c04ca80 Merge pull request #1540 from tavrez/patch-1
d32e20bc nghttpx: Make sure that Pool gets cleared when all buffers are returned
8b8ba6b0 Merge pull request #1542 from nghttp2/nghttpx-check-sigalg
81fb0153 nghttpx: Choose ECDSA cert if compatible signature algorithm available
d8c71d5f Added new nghttp2_ksl.c to Windows makefile
fb5b5aef Merge pull request #1537 from nghttp2/nghttpx-allow-colon-in-pattern
6787423e nghttpx: Add workaround to include ':' in backend pattern
ffcdf5df Merge pull request #1533 from LorenzNickel/patch-1
0cdb1738 Fix typo in security.rst
c9d5472f Bump version number to 1.43.0-DEV
15bd71ed Update manual pages

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>