More clouds layer

[Rivmun]

Learning from elytra aeronautics, maybe.

[Rivmun]

Partial Implementation in #6 v1.2.0 in a way of make clouds thicker.

[Rivmun]

In 1.7.0, the code is technically supports to gen more layers of clouds, but it will DOOM hardware. No impl this function till I find a way to improved performance.

[Rivmun]

Finally implement culling in 1.7.2 #57 and we can now try to add more cloud layers for SFCR. To add more fully customized clouds layer instead of just add a solid static one, needs to adjust a lot of code nearly rework whole mod. Its complex is goes beyond my expectation. I need more time to doing with it.

[Rivmun]

Some thought:

• Needs a data structure to carry every face position and it cannot be too redundance. It's will benefit to more layer performance.
• Needs rewrite sample method to do a fast sample instead of foreach one that now in use.
  • Idea is: sample some isolated points in range of cloud render zone, then spread from that point to a slice of clouds.
  • Updating no longer update whole clouds layer instead of a slice. When player move across a unit of clouds size, only generate clouds in boundary instead of whole layer.

Because 1.7.6 is quite big change, I need to rework 1.8.x-dev which is in my local repo.