Rewrite SpriteList to use an internal sprites array

[dmitrizagidulin]

ippa, Here's the SpriteList rewrite, plus some more tests to go with it.

Things to note:

• Now uses an internal array called 'sprites' to store the sprites, instead of using Array in its prototype chain
• Implements the full Array API, delegates calls to the 'sprites' attribute
• I added tests to make sure the new sprite lists work with collision detection
• The only thing that this breaks is direct array-like access, ie sprite_list[0] (this is replaced, for the few internal methods that need it, with sprite_list.at(0) ). This is a bit unfortunate, but I don't see how it can be avoided.

This could stand to have a lot more jsdocs / function comments, but I wanted to first run this by you, before putting those in.

[ippa]

Excellent work!

[ippa]

I think we can refer ppl to mozillas Array docs for all the methods you've implemented instead of writing big explanations for each method.. I see you implemented a lot of them :)

[dmitrizagidulin]

Good call (re link people to docs) :)