Pyneb

Correct bug in utils/manage_atomic_data/extract_flt : bytes and str confusion.

Change the way the low and High density ratios are obtained. Old way was using the statistical weights ratio, but this only works for S+-type of density diagnostics. Not for IR line ratios.
Add a Notebook in the doc directory to explore Critical densities.

* Add a MonteCarlo_and_ANN notebook to show the use of Neural Network when a lot of data is used.
* manage Poly and CatBoost as method for the getTemDen ANN
* Some refactoring

* Fix the last np.float to np.float64 in pynebcore and misc
* Correct bug in ICF of S+, allow it again (it was set unavailable)

* Remove the old doxygen configuration files and install new schema to build the documentation
* Create updatePyNeb.md that lists the process to make a new realease.
* Accept He2 and He3 in icf.getElemAbundances atom_abun keyword.
* Add HI density keyword to Atom/getIonAbundance method.
* Remove test on numpy version from __init__.py
* important updates to the FeII and FeIII atomic data, coherent with the paper published in Atoms Mendoza+23
* Add a python jupyter Notebook to support the answer to Ueta+Otsuka 2022 paper on Attenuation correction

* emisGrid/plotContours now have a level keyword.
* N3r and N5r added to LINE_LABEL_LIST dictionnary defined in utils/init.py
* o_i_coll_ZT03 added to atomic data
* HeI labels now have a dot after the wavelength (ex: 4471. instead of 4471)
* IPs from utils/physics are now generated also for H and He
recombination lines can now be used in emisGrid
* parseAtom2 returns rec='r' code to identify recombination atoms
* Some minor bugs corrected

* Add the option of using Artificial Neural Network to speed-up getCrossTemDen. This implies the library AI4neb is installed (https://github.com/Morisset/AI4neb) with Tensorflow and Scikit-learn. This will be described in a forthcoming paper, any information can be asked using the Google group.

* File requierements.dev added to root directory (only for developpers).
* A lot of docstrings have been modified to prepare the API documentation
* Directory pyneb/docs reorganized
* A workflow directory is added to automatize the API documentation (all this from MJChimal fork)