fix input_device_description_to_s()
add DirectFB::SurfaceDescription
ファイル構成を変更
implement DirectFB#create_surface()
implemate Surface#stretch_blit
update example/blue_rectangle.rb
fix create_surface
description を見直し
update surface
implement DirectFB::Font
DFBFontDescription 関連の処理を追加
add DirectFB::Rectangle
add DirectFB::Font
impement DirectFB#create_font()
implement DirectFB::Surface font methods
add example/text.rb
add example/simple.rb
update DirectFB::Surface
mod surface description
add mrb_directfb_image_description_new() / mrb_directfb_image_description_get()