- Added flags for A_Fade functions:

- FTF_REMOVE: Removes the actor when the alpha hits a certain level.
- - A_FadeIn - 1.0
- - A_FadeOut - 0.0
- - A_FadeTo - Alpha target level reached
- FTF_CLAMP: Locks the alpha to the range [0.0, 1.0]. This can be used to fix the alpha in case it goes over the threshold as well.