upgrade to version 1.3.0

[BDonnot]

• [BREAKING] GymConverter has been moved to grid2op.gym_compat module instead of grid2op.Converter
• [FIXED] wrong computation of voltage magnitude at extremity of powerlines when the powerlines were disconnected.
• [FIXED] rte-france#151 : modification of observation attributes 3
  could lead to crash
• [FIXED] rte-france#153 : negative generator could happen in some
  cases
• [FIXED] an error that lead to wrong normalization of some generator (due to slack bus) when using the
  gymconverter.
• [FIXED] a bug that prevented runner to read back previously stored data (and now a test to check
  backward compatibility down to version 1.0.0)
• [FIXED] small issue that could lead to non reproducibility when shuffling chronics
• [FIXED] a bug in obs.bus_connectivity_matrix() when powerlines were disconnected
• [ADDED] a class to deactivate the maintenance and hazards in the chronics from file
  GridStateFromFileWithForecastsWithoutMaintenance
• [ADDED] a keyword argument in the matplotlib plot information on the grid
  (plot_helper.plot_info(..., coloring=...))
• [ADDED] a function to change the color palette of powerlines (plot_helper.assign_line_palette)
• [ADDED] a function to change the color palette of generators (plot_helper.assign_gen_palette)
• [ADDED] Support the attack of the opponent in the EpisodeData class
• [ADDED] Now the observations are set to a "game over" state when a game over occurred
  see BaseObservation.set_game_over
• [ADDED] a method to plot the redispatching state of the grid PlotMatplot.plot_current_dispatch
• [ADDED] the documentation of Episode module that was not displayed.
• [IMPROVED] silence the warning issue when calling MultiEnv.get_seeds
• [IMPROVED] the tolerance of the redispatching algorithm is now more consistent between the precision of the solver
  used and the time when it's
• [IMPROVED] make faster and more robust the optimization routine used during redispatching
• [IMPROVED] error message when the state fails because of infeasible redispatching