Changes

• StatOnce and StatExists removed.

These were legacy items and should be replaced by either Prioritized or Attribute.

• StatIntFraction and StatIntFloatMul is merged into StatIntRounded which supports both float and fraction multipliers.

• StatFlags is now a newtype.

• StatCache removed, this was a pretty useless implementation, users should implement caching based on their own needs.

• Prioritized's default value now has i32::MIN priority. By default the type now fetches the last occurrence instead of the first.