Changed how lighting/unlighting tiles worked.

Made it so that the tiles only toggle when the test random number is
less than the duty parameter. This makes the color changing a little smoother.
Changed tile size and spacing.
Added a task list to the README.md file.
Added XCode checkout file to the repo.
Moved Tile.{h,cpp}.

These were incorrectly created in the xcode directory. Moved them
into the src directory and re-added them to the XCode project.