Update README.md

Purely symbolic promotion from alpha to beta, due to expanded testing.

Added an option to enable or disable bloom

This configuration option is named "enable_bloom", and defaults to true.

Tweaked gaussian blur kernels

Previously, the gaussian blur kernels were actually bimodal due to a typo. This obviously isn't correct, and it has been fixed.

Implemented HUD scaling

Added 16-bit mat support to the material pack compiler

Update compile.md

Added notes about displacement maps.

Added SSAO

Added screen-space ambient occlusion.

Some more materials/compiler cleanup

Discovered some minor issues while preparing the material compiler
documentation. These issues have been corrected.

Updated the readme to point to the material compiler documentation.

Switched to VBO orphaning

This change appears to fix an inscrutable graphics corruption issue that
looked suspiciously like a driver synchronization bug. VBO orphaning is
the correct approach here, anyway.

Renderer implementation of materials

The renderer now implements all material properties. There are some
inconsistencies around alpha mode handling: level geometry is forced
opaque, and transparent geometry is forced to blend, in order to
accommodate JK's vertex alpha. Effectively, the opaque and blend alpha
modes do the same thing right now, so they may be deleted in a future
version.

This change also includes a sample material pack that modders can use as
a base for their own work. Most notably, this material pack provides a
simple emissive lightsaber material.