Decimal conversion of Number to zt-string (still not precise enough). Zt-string copy and length calculation helpers.

src/libecmaobjects/ecma-globals.h

@@ -527,6 +527,11 @@ typedef double ecma_number_t;
  */
 #define ECMA_NUMBER_ONE  ((ecma_number_t) 1)
 
+/**
+ * Null character (zt-string end marker)
+ */
+#define ECMA_CHAR_NULL  ((ecma_char_t) '\0')
+
 /**
  * Maximum number of characters in string representation of ecma-number
  */