[c++ / SFML] [µPaint][2] A simple drawing program

A simple drawing program created using c++ and SFML. For more detail see:
Part 1: https://steemit.com/steemstem/@numbo/c-sfml-paint-a-simple-drawing-program
Part 2: https://steemit.com/de-stem/@numbo/c-sfml-paint-2-ein-minimalistisches-zeichenprogramm