v1.0.0: Update to Gym v0.26 and new mujoco bindings

This new release comes with the following changes:

• Compatibility with gym v0.26. Previous gym versions won't be compatible with this release. @rodrigodelazcano
• Added new environment versions that depend on the new mujoco python bindings. @rodrigodelazcano
• Old environment versions that depend on mujoco_py are still kept but will be unmaintained moving forward. @rodrigodelazcano
• New utility methods for GoalEnv class as suggested in #16 . compute_terminated and compute_truncated @rodrigodelazcano

The new versions of the environments that depend on mujoco bindings were validated with respect to the old versions of mujoco_py. The benchmark was performed using TQC + HER (sb3 implementation) with the same hyperparameters for both environment versions. The results can be seen here: https://wandb.ai/rodrigodelazcano/gym_robotics/reports/Benchmark-Gym-Robotics-SB3--VmlldzoyMjc3Mzkw