parameterize number of dimensions of vector in tvec<D, T, P>

- specializes for 1, 2, 3 and 4-dimensional vector types
  which are then aliased as tvec1, tvec2, tvec3 and tvec4
- requires C++11 aliases; breaks compatability with C++03
- tested on:
  - clang-3.5.2, clang-3.8.0
  - gcc 4.8.5, gcc 5.4.1, gcc 6.2.0

TODO:
- still uses template template parameters - most can probably be removed
- some definitions might now be de-duplicated

test/external/gli/core/levels.inl

@@ -3,8 +3,8 @@
 
 namespace gli
 {
-	template <typename T, precision P, template <typename, precision> class vecType>
-	inline T levels(vecType<T, P> const& Extent)
+	template <int D, typename T, precision P, template <int, typename, precision> class vecType>
+	inline T levels(vecType<D, T, P> const& Extent)
 	{
 		return glm::log2(compMax(Extent)) + static_cast<T>(1);
 	}