Migrate camera doc to 4 0 0

[kaltinril]

1. Added folders:
   1. /docs/features/Camera
   2. /docs/features/Camera/OthograhicCamera
2. Pulled in old documentation from Archived/Cameras
3. Split documentation into Camera/OrthograhicCamera pages.
   1. Created camera.md
   2. Created Camera/OrthographicCamera.md
4. Created 2 simple diagram/images
   1. If you don't want them I can remove them.
5. Added more information to the Camera page
6. Added more details and examples to the OrthographicCamera page:
   1. Creating an instance
   2. Moving the camera
   3. Zooming the camera
   4. Rotating the camera

Related Sample code pr: craftworkgames/MonoGame.Extended-samples#14

[AristurtleDev]

Two small changes requested. Regardless, good work, and thank you for the contribution.