Populated and updated the definitions using text observation distributions.

[devjwsong]

• Generated the text observation distributions and fixed any inconsistencies.
• Changed the way to define the descriptions, action spaces, and action exclusiveness. (Refer to README.md.)
  • We don't have to define the descriptions for all environments. If there is no environment name in DESCRIPTIONS, the text observation is used as the environment name and description.
  • We don't have to define the action spaces for all environments. We can define a single action space called "default" to be shared for all environments.
  • We don't have to define the action exclusiveness for all environments. We can define a single action exclusiveness called "default" to be shared for all environments.

[pranavguru]

lgtm, great work!