add NaN check for normal information

+fix bug in tangent calculation
+add PBR approach for units with no pre-calculated tangent
+remove wound texture which no longer needed


now support a new PBR approach called "PBR Lite"
Sample mtl file:
{material bump
{diffuse "$/model/m1a2tusk_new/turret"} ;base color
{bump "$/model/m1a2tusk_new/turret_n"} ;normal
{specular "$/model/m1a2tusk_new/turret_mra"} ;metallic/roughness/ao
{height "$/envmap/env"}
{blend none}
{full_specular}
}


this will work for models which do not have bump textures.

hotfix

fix bug in light.hlsl

+optimize code

+refactor light.inc

+fix bug in vs TBN calculation

+fix bug in shadow

fix bug of rendering issue in inventory

+remove old reference asset

+add a pack of pbr example assets

+improve EnvironmentColor function and indirect light calculation

fix bug when no bump is provided in pure PBR mode

update english license

update license