Typo
Optimize flake areas

So far, we've been drawing all flakes in canvas of the size of the
original randomly drawn flake.

All following flakes of the size-canvas-array are smaller than that.

Now we just use the smaller size of the projected flake image plus
2 times the current blur value as size.

This has the added advantage that we keep the calculated flake sizes
as canvas sizes. We will need that for our next step.
Reenable uglifying the js build
Add slight speed differences

Make flakes always have 3/4 of the given speed value plus 1/4 randomly.

This makes flakes on the same plane fall slightly different in regards
to each other which looks more natural, I think.
Add NUM_FLAKE_LAYERS

NUM_FLAKE_KINDS was also used inappropriately for the number of layers
to use while it was hardcoded potentially differently elsewhere

We introduce the new constant and make opts.zSteps refer to that and
fix the incorrect references to it.

We adjust the number of layers to 10.
Fix flake distribution

Assigning each layer the same amount of flakes looks right on first glance
but is actually wrong. The on-screen size of the further away layers
is larger than the closer ones.

Our previous approach leads to flakes becoming ever more sparsely present
on each following layer.

We fix that by introducing a simple weighted distribution where every
layer's weight is the current layer size, divided by largest.
Add link to github project page
IDEA files