added Unicode_To_Utf8 converter

h2/lib/h2-utf8.ads

@@ -0,0 +1,20 @@
+generic 
+	type Unicode_Character_Type is (<>);
+	type UTF8_Character_Type is (<>);
+package H2.UTF8 is
+
+	Invalid_Unicode_Character: exception;
+
+	subtype Unicode_Character is Unicode_Character_Type;
+	subtype UTF8_Character is UTF8_Character_Type;
+
+	type UTF8_String is array(System_Index range<>) of UTF8_Character;
+	type Unicode_String is array(System_Index range<>) of Unicode_Character;
+
+	function Unicode_To_UTF8 (UC: in Unicode_Character) return UTF8_String;
+	function Unicode_To_UTF8 (US: in Unicode_String) return UTF8_String;
+
+	--procedure UTF8_To_Unicode (UTF8: in UTF8_String;
+	--                           UC:   out Unicode_Character_Type);
+
+end H2.UTF8;