Fix perspective

When running this in chrome the rectangles didn't move up and
down the y-axis, only circling in the x axis. I don't fully
understand what this code does, but it seems applying z_delta
to the z-axis doesn't yield the (I presume) intended effect
of the wings moving up and down. Changing this to instead
apply to the y-axis yields a good result.

The factor is something I chose because It Looked Good on My
Machine (tm) but it can probably be something smarter.
Fix perspective transform.

Marcus Stade noticed that the z-component of the transform was having no effect; this was because the perpspective transform on the camera was getting truncated. This change sets "-webkit-transform-style: preserve-3d" on the camera so that the transform doesn't get flattened. It also shrinks the magnitude of the z translation a bit and adds a rotation to the camera.

Conflicts:
	ep.js
Up the z amplitude a bit and lower the camera position

It looked a bit squashed with the lower amp so I put it back
up. But I did so while making it view dependent, so that it
doesn't shoot up in the sky if the window is resized. It also
didn't look positioned quite right so I dropped
the camera a bit by putting it at `top: 25%`.

I also changed the rectangle width/height to use `vmin`
instead of percentages. This ensures that they stay square,
regardless of the width/height of the window.

Finally, I changed the camera perspective value to give a more
orthographic look, which made it more alike the recollection
I have of the original.

Man I love this thing.
Merge branch 'master' of https://github.com/mstade/elektropaintjs into mstade-master

I hoisted the read of window.innerHeight out of the loop, too (I generally do this to avoid style recalc thrashing, though that probably would happen with document.body.offsetHeight rather than window.innerHeight...).

Conflicts:
	ep.html
	ep.js