Rewrote material loader
Rewrite of material loading to use the github.com/golang-source-engine/vmt package.
- Updated KeyValues package to better support some vmt edge cases
- Remove internal logging from the material loading process
- Removed
resource/
import from vmt and vtf loading. Now only used by the material loading functions. Vmt and Vtf loading functions are exposed, so loading materials without using theresource/
package is considerably easier.