Add image uploads

[AlphaRLee]

Students enjoy using images for characters in their games

AC:

• Add an image("file_name.png", x, y, width, height) function
• Draw the image at the given x and y and selected width and height
• If width and height are negative, invert the picture and draw to the left/above the X/Y respectively
• Must work with extensions being case-insensitive (e.g. works with .PnG)
• Restrict image() to only accept .png, .jpg, .jpeg .svg - maybe there's a way to get the HTML image types on the input
  • Look into adding .gif and/or .webp, not hard requirement
• Unit tests
  • Test bad file types and bad file names
• Docs