Filling Polygons
-Be sure to complete each piece of the readme

  In this project you will fill polygons using the Edge Table and
Active Edge Table technique. These methods are capable of filling
concave and self-intersecting polygons which makes them very robust
(more robust than OpenGL). For the purposes of this project you should
do the following.

- Create a struct to hold polygons (simply a vector of Points)

- Allow multiple 2D polygons to be displayed on the screen (keep a
  vector of polygons to help with this)

- Include a method of creating polygons via the mouse. Use left click
  to add points to the polygon and right click to 'finish' or end a
  polygon.

Extra credit tools:
- 'r' to remove the last polygon entered - easy
- 'c' to clear all polygons - easy
- Enable rubberbanding via passive mouse motion in between clicks. - medium