/*
 * Draw a string with the given Imlib2::Font at the specified coordinates
 *
 * Examples:
 *   font = Imlib2::Font.new 'helvetica/12'
 *   string = 'the blue crow flies at midnight'
 *   image.draw_text font, string, 10, 10
 *
 *   # draw text in a specified color
 *   font = Imlib2::Font.new 'helvetica/12'
 *   string = 'the blue crow flies at midnight'
 *   color = Imlib2::Color::AQUA
 *   image.draw_text font, string, 10, 10, color
 *
 *   # draw text in a specified direction
 *   font = Imlib2::Font.new 'verdana/24'
 *   string = 'the blue crow flies at midnight'
 *   color = Imlib2::Color::YELLOW
 *   direction = Imlib2::Direction::DOWN
 *   image.draw_text font, string, 10, 10, color, direction
 *
 *   # draw text with return metrics
 *   font = Imlib2::Font.new 'arial/36'
 *   string = 'the blue crow flies at midnight'
 *   color = Imlib2::Color::PURPLE
 *   direction = Imlib2::Direction::LEFT
 *   metrics = image.draw_text font, string, 10, 10, color, direction
 *   ['width', 'height', 'horiz_advance', 'vert_advance'].each_index { |i, v|
 *     puts v << ' = ' << metrics[i]
 *   }
 *
 */ 
static VALUE image_draw_text(int argc, VALUE *argv, VALUE self) {