Added startsWithDouble() method on ZString.

ZString.cpp

@@ -267,6 +267,15 @@ namespace coreutils {
       return strncmp(cursor, value, strlen(value)) == 0;
    }
 
+   bool ZString::startsWithDouble() {
+      push();
+      char *tempc = cursor;
+      double temp = strtod(cursor, &cursor);
+      int diff = cursor - tempc;
+      pop();
+      return diff != 0;
+   }
+
    int ZString::compare(ZString zstring) {
       char *end1 = data + length;
       char *end2 = zstring.getData() + zstring.getLength();