Add a file movies.py with functions to create movies from Aevol dumps.

Function treat_generation takes a dump file (structure: one line per individual structured as follow: 'posx \t posy \t
value') and writes a png (one pixel per individual, lossless compression).

Main function calls treat_generation for each generation then gathers
the pngs in one movie (10x10 pixels per individual, with appropriate
interpolation).
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