/* 
 * Get the horizontal and vertical advance of the given string using
 * this font.
 *
 * Example:
 *   font = Imlib2::Font.new 'verdana/36'
 *   advances = font.advance "what's my advance?"
 *   ['horizontal', 'vertical'].each_index { |i, v|
 *     puts 'text ' << v << ' advance = ' << advances[i]
 *   }
 *
 */
static VALUE font_text_advance(VALUE self, VALUE text) {