Missing license for GLM

[mfansler]

GLM is used but no copy of its license appears to be redistributed. Note that this is a requirement of the license:

"The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software."

Please include a copy of the license.

[mfansler]

Note that stb is Unlicense (it has no copy requirement) and the sources from miniply and tinyobjloader include license copies directly.