make the move subpixel
remove the old unused cloud_move
separate the three clouds' moves, both the yoffset, the x speed and the x start time (with a time offset)
remove two blank images (useless and slower than Null())
clarify in weather.rpy which are images directly shown on the screen and not just ingredients for the others
simplify the screen code
* Reimplemented weather using renpy image methods
* Fixed weather causing fps drop
* Added cached weather results to the main room
* Reduced animation overhead
* Removed weather screen
* Unified day and night cloud images
