New Magic tool: Reflection
Click to make a reflection of what's above the cursor,
below the cursor.
Click and drag down to stretch the lower reflection, or
drag up to make an reflection of the bottom of the picture
above where you clicked.
Or, drag left or right to make a reflection on the left of
what's on the right, or vice-versa.
It's not perfect, but my math skills are failing me, and it's
probably suitable.
Demo videos posted to Twitter
* https://twitter.com/TuxPaintTweets/status/1456541738667954181
* https://twitter.com/TuxPaintTweets/status/1456542229376294924
Closes https://sourceforge.net/p/tuxpaint/feature-requests/202/
