refactor pybullet/gym to allow instantiating environments directly from a pybullet install:

work-in-progress (need to add missing data files, fix paths etc)

example:

pip install pybullet
pip install gym

python
import gym
import pybullet
import pybullet_envs
env = gym.make("HumanoidBulletEnv-v0")

examples/pybullet/gym/pybullet_envs/data/mjcf/ground_plane.xml

@@ -0,0 +1,5 @@
+<mujoco model="ground_plane">
+  <worldbody>
+    <geom conaffinity="1" condim="3" name="floor" friction="0.8 0.1 0.1" pos="0 0 0" type="plane"/>
+  </worldbody>
+</mujoco>