Features:

- Add analysis


Fixes/Enhancement:

- Have a try with SGE instead of SDL_gfx (benchmark both)
- Use cairo_surface_create_for_image instead of SDL_image
- Do note preload all the songs at screen_song
- Add the drawing resolution (draw small surfaces and then zoom to the
  rendering bigger surface)
- Add binary dump of the songs (to speed up directory browsing)
- Use a cross platform input sound library (portAudio ?)
- Add an in-game configuration screen (with config file in 
  $HOME/.ultrastar-ng)

Change songs directory structure :

+- songs
   +- category_1
   |  +- category_1.png (cover of the category)
   |  +- song_1
   |  |  +- song_1.txt
   |  |  +- backgroung.png (name given in #BACKGROUND directive of song_1.txt)
   |  |  +- song.mp3 (name given in #MP3 directive of song_1.txt)
   |  |  +- song.mpg (name given in #VIDEO directive of song_1.txt)
   |  |  +- cover.png (name given in #COVER directive of song_1.txt)
   |  +- song_2
   |  +- ...
   |  +- song_n
   +- category_2
   +- ...
   +- category_n

screns browsing :

Intro
 +-> Choose category
   +-> Choose song (and level)
     +-> Sing
       +-> Score
         +-> Go back to Choose song
 +-> Configuration
   +-> Configure sound
     +-> Choose sound card
     +-> Music level
     +-> Mic level
     +-> Mic fft sensibility ( in db with db-meter )
   +-> Configure theme
   +-> etc.
 +-> Accorder (for guitar for example)
 +-> Song composer/modifier
 +-> Quit
