append_len
Description:
Appends len bytes of val to this.
If len is positive, val may contain embedded nuls and need not be nul-terminated. It is the caller's responsibility 
      to ensure that val has at least len addressable bytes.
If len is negative, val must be nul-terminated and len is considered to request the entire string 
      length. This makes append_len equivalent to append
      .
Example: Append n bytes of a string:
public static int main (string[] args) {
	// Output: ``hello, world!``
	StringBuilder subbuilder = new StringBuilder ("hello");
	StringBuilder builder = new StringBuilder ();
	builder.append_len (subbuilder.str, subbuilder.len);
	builder.append_len (", world!\n", 9);
	print (builder.str);
	return 0;
}
    
    valac --pkg glib-2.0 GLib.StringBuilder.append_len.vala
    Parameters:
| this | |
| val | 
           bytes to append  | 
      
| len | 
           number of bytes of   | 
      
Returns:
| 
           this  |