PFE 0.5.1b

Changelog:

0.5.1b:

 - Gutted pxlfst.voxel.Block of it's unnecessary variables.

 - Added a texture parameter to pxlfst.inventory.inv.EItem's constructor as it was passing a test texture previously.

 - Added deltaTime parameter to pxlfst.core.vis.renderables.Renderable's render method for how long the current frame is meant to represent.

 - Created pxlfst.core.vis.img.AnimatedTexture, this is a texture that represents an animation, frames oriented vertically.

 - pxlfst.core.vis.img.Texture and AnimatedTexture use the deltaTime parameter in their getImg methods. This progresses the frames of an animated texture without needing to cast or use instanceof. The base getImg method is still available.

Bugs:

PFB-0001a: deltaTime is not passed properly to Renderables, causing frametime dilation on AnimatedTextures. [will fix tomorrow]