Feature : glm operator* for mat4 and vec3

Heya!

One thing we had before with ofMatrix4x4 was an operator like

template <typename T, precision P>
inline tvec3<T, P> operator*(const tmat4x4<T, P>& mat, const tvec3<T, P>& vec3) {
    return (tvec3<T, P>) (mat * tvec4<T, P>(vec3, 1.0));
}

This means that for vec3's we can just do mat * vec3 and get a vec3 result

Currently with glm we've lost this, and need to explicitly inflate to a vec4 and back down to a vec3 every time we want to transform a vec3 by a matrix.

Any takers?

The issue names no files, tests, or entry points. Start by locating the GLM matrix and vector operator definitions used by openFrameworks, then verify the requested mat4 * vec3 behavior against the existing C++ test coverage; done means that expression returns a vec3 without explicit conversion.