Moved Domain enum to separate header

For clarity, this moves the Domain enum class to a separate header,
because it’s not just variable-specific but also applicable to
functions, for example.

include/anthem/AST.h

@@ -2,6 +2,7 @@
 #define __ANTHEM__AST_H
 
 #include <anthem/ASTForward.h>
+#include <anthem/Domain.h>
 #include <anthem/Tristate.h>
 
 namespace anthem
@@ -353,13 +354,6 @@ struct VariableDeclaration
 		Body
 	};
 
-	enum class Domain
-	{
-		Unknown,
-		General,
-		Integer
-	};
-
 	explicit VariableDeclaration(Type type)
 	:	type{type},
 		domain{Domain::Unknown}

include/anthem/Domain.h

@@ -0,0 +1,27 @@
+#ifndef __ANTHEM__DOMAIN_H
+#define __ANTHEM__DOMAIN_H
+
+namespace anthem
+{
+namespace ast
+{
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// Domain
+//
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+enum class Domain
+{
+	General,
+	Integer,
+	Unknown,
+};
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+}
+}
+
+#endif