[CGMZ] Core - Version 1.21.0

Hi all, today this plugin was updated to version 1.21.0!

A new function to calculate the battler average level was added, which will help some [CGMZ] plugins provide additional options when calculating the party level. Another function to get a sprite's bitmap with effects applied was also added, which can make it easier to show a bitmap image instead of a full sprite in some cases.

A bug was fixed with a function for converting time to a string as well, though this function is not currently used in any [CGMZ] plugins.

• Added utility function to calculate the average level of battle actors
• Added utility function to get sprite bitmap after effects applied
• Fix bug with time to string function