Add static constants for vec1

- Tests, too

glm/detail/type_vec1.hpp

@@ -59,6 +59,8 @@ namespace glm
 			static GLM_RELAXED_CONSTEXPR precision prec = P;
 #		endif//GLM_META_PROG_HELPERS
 
+		static const type ZERO;
+		static const type X;
 		// -- Data --
 
 #		if GLM_HAS_ANONYMOUS_UNION

glm/detail/type_vec1.inl

@@ -32,6 +32,11 @@
 
 namespace glm
 {
+	template<typename T, precision P>
+	const tvec1<T, P> tvec1<T, P>::X = tvec1<T, P>(static_cast<T>(1));
+
+	template<typename T, precision P>
+	const tvec1<T, P> tvec1<T, P>::ZERO = tvec1<T, P>(static_cast<T>(0));
 	// -- Implicit basic constructors --
 
 #	if !GLM_HAS_DEFAULTED_FUNCTIONS || !defined(GLM_FORCE_NO_CTOR_INIT)