Leggedsnake

- ``evolutionary_optimization`` function is removed. Use ``GeneticOptimization`` class instead.
- You can no longer use the argument "init_pop" to change the size of the initial population.
It now always set to max_pop.
- ``time_coef``, ``calc_rate`` and ``max_sub`` parameters of ``params["simul"]`` replaced by a unique
``physics_period`` set to 0.02 (s).
- ``leggedsnake/Population evolution.json`` removed.
It contained data about an evolution run and is not relevant for users.

- The main example file ``strider.py`` was launching animations for each subprocess.
This file is now considered an executable.
- ``evolutionary_optimization_builtin`` was during the last evaluation of linkages.
- ``data_descriptors`` were not save for the first line of data only in
``geneticoptimizer``.
- Multiple grammar corrections.
- The ``video`` function of ``physicsengine.py`` now effectively launches the video (no call to plt.show required).
- The ``video`` function of ``physicsengine.py`` using ``debug=True`` was crashing.

- Native support for PyGAD is no longer present.
- ``evolutionnary_optimization`` (replaced by ``evolutionary_optimization``).
- Data saved in the old txt format are no longer readable (were they readable?)

- Explicit dependency to PyGAD. There is no longer an annoying message when
PyGAD is not installed.