Add better documentation to the Canvas module.
Add better documentation to the Canvas module.

Ignore-this: ba7ba9842faa1c5e83b33ac2d9ad1ce7

darcs-hash:20141113221723-4d2ae-7c0b48e341a2965f700bf8310cf998138b0abac1

johntyree/HsQML,johntyree/HsQML