Merge pull request #985 from dgough/next

Updated encoder usage text
Removed #ifdef USE_FBX from the encoder
Updated the encoder to always write material names in the GPB file
Material names will now be written in the GPB even if "-m" is not passed as an argument.
The purpose of this change is that people could use "-m" to create their initial material file but then later update their GPB file without needing to overwrite their material file.