old_contents: def mujoco():
      return dict(
          nsteps=2048,
          nminibatches=32,
          lam=0.95,
          gamma=0.99,
          noptepochs=10,
          log_interval=1,
          ent_coef=0.0,
          lr=lambda f: 3e-4 * f,
          cliprange=0.2,
          value_network='copy'
      )
  
  def atari():
      return dict(
          nsteps=128, nminibatches=4,
          lam=0.95, gamma=0.99, noptepochs=4, log_interval=1,
          ent_coef=.01,
          lr=lambda f : f * 2.5e-4,
          cliprange=lambda f : f * 0.1,
      )
  
new_contents: def mujoco():
      return dict(
          nsteps=2048,
          nminibatches=32,
          lam=0.95,
          gamma=0.99,
          noptepochs=10,
          log_interval=1,
          ent_coef=0.0,
          lr=lambda f: 3e-4 * f,
          cliprange=0.2,
          value_network='copy'
      )
  
  def atari():
      return dict(
          nsteps=128, nminibatches=4,
          lam=0.95, gamma=0.99, noptepochs=4, log_interval=1,
          ent_coef=.01,
          lr=lambda f : f * 2.5e-4,
          cliprange=lambda f : f * 0.1,
      )
  
  def retro():
      return atari()
  
subject: Add retro to ppo2 defaults (#682)