As per https://peps.python.org/pep-0394/, the python binary can be one
of the following options:
- Python 2
- Python 3
- Not exist
All of the scripts in libxml2 use 'python', which may not exist.
As Python 2 reached EOL on the 1st January 2020, it's safe to move the
scripts to use python3 explicitly.
* tree.c: improving some documentation comments
* xmlregexp.c: found and fixed a mem leak with python regression tests
* doc/*: rebuilt the doc and the API XML file including the
xmlregexp.h xmlautomata.h and xmlunicode.h headers
* python/generator.py python/libxml2class.txt python/libxml_wrap.h
python/types.c: added access to the XML Schemas regexps from
python
* python/tests/Makefile.am python/tests/regexp.py: added a
simple regexp bindings test
Daniel