Moved board and boardRenderer to Game class
Moved update() function to Game class
Create Game object in main.html

main.js contained only code to create a canvas element and the Game
object, so this has been moved to a <script> tag in the main page.  The
canvas element will eventually be declared with a tag so that it can be
positioned, etc.
Declare canvas with a tag

Add a <canvas> tag to main.html rather than creating it explicitly in
script