Various small typo fixes and clearing up

[enbyspiders]

Change "HaxePunk.svg" to "icon.svg" to make it clear it is the icon that
the application is going to use.
MainScene should say "override public function" not "public override
function".
It's not spelled "HaXe" anymore.

[ibilon]

+1 for the rename of the icon, it does make it clearer. The correction of haxe is ok too.

For the "override public function" vs "public override function" it's more of a preference I think, personally I write it the 2nd way.

Regardless of choice it needs to be the same as the haxelib run's template.
(we should update the icon there too)

[enbyspiders]

Regrading the "override" I didn't even know you could switch those up, I really thought it was a typo. :) But in that case I guess it doesn't matter much if there is no general consensus how it should be written.
I agree that it should be the same across all examples/templates and since it is written "public override function" in the tutorial on the website as well, I'll change it back again.
EDIT: Saying that I just saw that in Main.hx.template it says "override public function init()", so should I change this one too, or keep both with "override" being first? This is also the same at the haxelib template.