Grid2op

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- [ADDED] better handling of serialization of scenarios.

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- [ADDED] parrallel processing of the environment: evaluation in parrallel of the same agent in different environments.
- [ADDED] a way to shuffle the order in which different chronics are read from the hard drive (see MultiFolder.shuffle)
- [FIXED] utility script to push docker file
- [FIXED] some tests were not passed on the main file, because of a file ignore by git.
- [FIXED] improve stability of pandapower backend.
- [UPDATED] avoid copying the grid to build observation

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- [ADDED] Adding a utility to retrieve the starting kit L2RPN 2019 competition.
- [ADDED] Layout of the powergrid graph of the substations for both the
`5bus_example` and the `CASE_14_L2RPN2019`.
- [FIXED] Runner skipped half the episode in some cases (sequential, even number of scenarios). Now fixed.
- [FIXED] Some typos on the notebook "getting_started\4-StudyYourAgent.ipynb".
- [FIXED] Error in the conversion of observation to dictionary. Twice the same keys were used
('time_next_maintenance') for both `time_next_maintenance` and `duration_next_maintenance`.
- [UPDATED] The first chronics that is processed by a runner is not the "first" one on the hardrive
(if sorted in alphabetical order)
- [UPDATED] Better layout of substation layout (in case of multiple nodes) in PlotGraph

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- [ADDED] extra tag 'all' to install all optional dependencies.
- [FIXED] issue in the documentation of BaseObservation, voltages are given in kV and not V.
- [FIXED] a bug in the runner that prevented the right chronics to be read, and output wrong names
- [FIXED] a bug preventing import if plotting packages where not installed, that causes the documentation to crash.

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- [BREAKING] BaseAction/Backend has been modified with the implementation of redispatching. If
you used a custom backend, you'll have to implement the "redispatching" part.
- [BREAKING] with the introduction of redispatching, old action space and observation space,
stored as json for example, will not be usable: action size and observation size
have been modified.
- [ADDED] A converter class that allows to pre-process observation, and post-process action
when given to an `BaseAgent`. This allows for more flexibility in the `action_space` and
`observation_space`.
- [ADDED] Adding another example notebook `getting_started/Example_5bus.ipynb`
- [ADDED] Adding another renderer for the live environment.
- [ADDED] Redispatching possibility for the environment
- [ADDED] More complete documentation of the representation of the powergrid
(see documentation of `Space`)
- [FIXED] A bug in the conversion from pair unit to kv in pandapower backend. Adding some tests for that too.
- [UPDATED] More complete documentation of the BaseAction class (with some examples)
- [UPDATED] More unit test for observations
- [UPDATED] Remove the TODO's already coded
- [UPDATED] GridStateFromFile can now read the starting date and the time interval of the chronics.
- [UPDATED] Documentation of BaseObservation: adding the units
(`issue 22 <https://github.com/Grid2Op/grid2op/issues/22>`_)
- [UPDATED] Notebook `getting_started/4_StudyYourAgent.ipynb` to use the converter now (much shorter and clearer)

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- [FIXED] Bug in L2RPN2019 settings, that had not been modified after the changes of version 0.4.2.