Some outstanding issues in PSFEx doc, and other notes:

- for html:
 . parameter list / description: should find a way to put this directly into
   the code, and extract the list with autodoc (aor something similar)
 . cross-references ... to figures, tables, sections ... and labelling
 . equation numbering / labelling / referencing
 . external references (aka citations to papers / bibtex ...)

- outstanding for pdf:
 . \mathbb unknown (but inserted by sphinx in building tex file)
 . \frac should be replaced (idem)
 . some issues with figure labels (?) Not clear how this should work: there are
   no obvious labelling commands (or is it \capstart?) in the sphinx-generated
   tex file.
   (looking at sphinx-generated tex file I note that labels for chapters /
   sections are automatically generated, but not for figures)
 . Figures are automatically numbered ... if built with figure directive.
   Not numbered with image directive (used to put figures in table in order to
   put two figures in same line ... Need a better way to do this

- Other points
 . optional titles in index.rst are used in html but not in pdf
 . :maxdepth: option is used in html but not in pdf
   idem for :caption: 
 ==> in pdf maxdepth is always 2 and title is always "CONTENTS"
 . figure numbering:  in pdf only (as chapt.numb) ...
   BUT: only "figures" are numbered, but not "images"
 . how to put two pngs into a single "figure" on the same line? 
   (I can put them as "images" in a table, but then they are not numbered in pdf)

