* Fix Sphinx warnings
howto/acro_forms.rst:4: WARNING: Title underline too short.
howto/acro_forms.rst:81: WARNING: Bullet list ends without a blank line; unexpected unindent.
howto/acro_forms.rst:88: WARNING: Bullet list ends without a blank line; unexpected unindent.
howto/acro_forms.rst:122: WARNING: Bullet list ends without a blank line; unexpected unindent.
tutorial/extract_pages.rst:6: WARNING: Failed to create a cross reference. A title or caption not found: api_extract_pages
* Fix documenting pdf2txt.py
reference/commandline.rst:12: ERROR: Module "tools.pdf2txt" has no attribute "maketheparser"
Incorrect argparse :module: or :func: values?
* Add CHANGELOG.md
Co-authored-by: Pieter Marsman <pietermarsman@gmail.com>