HDR lightmaps

[illwieckz]

To not confuse with adaptative lighting (#29).

It would be cool to implement HDR lighting.

@SomaZ has q3map2 patches to bake HDR lightmaps with q3map2:
https://github.com/SomaZ/GtkRadiant/commits/master

[illwieckz]

Dæmon engine claims to have EXR support. So, we may compile lightmaps with that HDR patch, convert them from RGBE .hdr to EXR .exr and attempt to load them.

[illwieckz]

XreaL's q3map2 fork also had code to produce HDR lightmaps, writing HDR PNG if I'm right.

[illwieckz]

For the record, ioquake3's renderergl2 has support for optional alternate HDR lightgrid (loading from external file maps/<mapname>/lightgrid.raw).