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.

tests/CMakeLists.txt

@@ -3,10 +3,10 @@ find_package(Criterion)
 add_executable(tests
 src/rse_math_tests.c)
 
-
-
 target_include_directories(tests PRIVATE
-${criterion_INCLUDE_DIR})
+${criterion_INCLUDE_DIR}
+${CMAKE_SOURCE_DIR})
 
 target_link_libraries(tests PRIVATE
-${criterion})
+${criterion}
+rse_graphics)