Benchmark result for A2C cartpole (#180)

* add benchmark spec files

* make dqn polyak

* specify resources

* update demo spec

* Updating a2c gae specs

* Update max cpus for a2c cartpole

* speedrun

* lower trial

* try save deepcopy of spec and info_space

* lower trial

* Updated a2c mlp specs

* Switch nstep separate to linear decay

* ramp up trial. problem confirmed fixed

* update lunar a2c search specs

* cleanup cartpole and lunar benchmark specs

* update demo spec to good params

* placeholder for experiment link

CONTRIBUTING.md

@@ -20,7 +20,7 @@ Reproducibility is crucial to deep RL, thus it is very valuable to have multiple
 1. a spec file
 2. a git SHA: check out the SLM Lab to the appropriate branch or commit
 
-An example experiment is [here](todo)
+An example experiment is [here](todo-pending)
 
 >The only aspect of experiments that are not reproducible are the random seeds. This is by design. Good algorithms and hyper-parameter settings should be reasonably stable across different random seeds.