Add my own math library

GLM works only for C++ and I plan on moving to back to C. There is
a C port, but it would be good for me to figure out vertex math myself.
Hence, my own library has been created.

cmake/Findglm.cmake

@@ -1,9 +0,0 @@
-set(GLM_DIR "${PROJECT_SOURCE_DIR}/third_party/GLM/")
-
-find_library(
-    glm
-    NAMES glm glm_shared
-    HINTS ${GLM_DIR}/build/glm
-)
-
-set(glm_INCLUDE_DIR "${GLM_DIR}/include")