Start project
Bootstrap basic files
Basic Game structure working
Add tick function and call it on each frame
Ad basic structures: Player, Bullets and Invaders
Create init function for initial setting up
Bugfix, w and h belong to canvas, not context
Call draw on each object
Add player movement and firing
Update and draw bullets
Remove bullets that leave the playground
Don't let player go outside of playground
Add invaders
Remove specific arrays, add collision detection

The specific arrays (si.bullets, si.players, si.invaders) born because I
wanted a way to control bullets. But there was no need for that since we
could have used splice and indexOf to target specific objects.
Bugfix, remove just one bullet

If splice doesn't get second argument it removes to the end of the
array.
Reduce bullets velocity

Also create them further from player.
Adapt center coordinates for fillRect function

fillRect starts drawing from top left corner, since we're using the
center coordinates for objects, we need to adapt them for fillRect.
Prepare for starfield background
Factor repeated code into a single function

The idea was to draw each object different, but I'll have these
rectangles for some time, so let's do things right.
Semantic change: no more bullets array now