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Add a "particle" material type

This has the effect of enabling point sprite mode and rendering mesh
geometry with DrawArrays(POINTS) instead of DrawElements(TRIANGLES).
This facility will enable the efficient reimplementation of the goal
and jump visuals.

Enabling this flag on basic-ball is a real surprise!
Tweaks to material effects

Fix additive material to support texture alpha.
Fix particle material to attenuate with distance according to perspective.
Add third light source to be used for sparkle effects
Replace goal and jump

The new goal and jump effects combine the new particle material effect with
the new sparkle light source to produce sparkly particles. This reduces
overdraw dramatically and improves performance significantly under fill
limited circumstances. The jump is now rendered in a single batch and the
goal is rendered in two.
Merge pull request #50 from rlk/newgoal

Merging a pull onto a branch. This will need testing before being merged to master.