Post-NeurIPS - `SequenceFitness`, `RmES`, `BatchStrategy`

Added

• Adds sequential problems (SeqMNIST and MNIST) to evaluation wrappers.
• Adds Acrobot task to GymFitness rollout wrappers.
• Adds modified Ant environment to Brax rollout.
• New strategies:
  • RmES (RmES following Li & Zhang, 2008).
  • Gradientless Descent (GLD following Golovin et al., 2020).
  • Simulated Annealing (SimAnneal following Rasdi Rere et al., 2015)
• Adds simultaneous batch strategy functionalities:
  • BatchStrategy: vmap/pmap distributed subpopulation rollout
  • Protocol: Communication protocol between subpopulations
  • MetaStrategy: Stack one ES on top of subpopulations to control hyperparameters

Changed

• Renamed crossover_rate to cross_over_rate in DE to make consistent with SimpleGA.
• Add option to add optional env_params to GymFitness, seq_length to addition and permute_seq for S-MNIST problem.
• Network classes now support different initializers for the kernels using the kernel_init_type string option. By default we follow flax's choice in lecun_normal.

Fixed

• Add spring_legacy option to Brax rollout wrappers.