Quick patch up to address a major bug and added objective markers as well.

- Bug fixed : Crouching makes you literally invisible to almost all enemy types!
- Objective markers for power crystals and exit doors have been added.
The objective markers should make it easier to know where you need to go to exit the level once you collect all power crystals.
- Some new art has been added to one of the starting levels. Its still a WIP. See the following blog post if you want to see pictures.

https://steemit.com/revulsion/@thecastle/revulsion-progress-for-the-night-objective-markers-and-new-art