* spot/tl/hierarchy.hh, spot/tl/hierarchy.cc (nesting_depth): New
function.
* python/spot/__init__.py: Also make it a method of formula in Python
* bin/common_output.cc, bin/common_output.hh: Implement
--stats=%[OP]n.
* NEWS: Mention it.
* tests/core/format.test, tests/python/formulas.ipynb: Test it.
* python/spot/__init__.py (show_mp_hierarchy, mp_hierarchy_svg): New
functions.
* tests/python/formulas.ipynb: Illustrate show_mp_hierarchy.
* python/ajax/spotcgi.in: Use mp_hierarchy_svg.
* python/ajax/css/trans.css: Adjust for possible overflows.
* NEWS: Mention this new feature.