Merge: Better synopses in many packages for a prettier catalog

This should fix/complete the synopses of my projects. The few cases left are where the doc is in the main module of a contrib without a readme, like with `header_keeper`. I'm not sure what to do with those yet, maybe simply removing the src folder.

I seizes this opportunity to improve the `extern_methods` example and create missing readme files. And also reorganized the mnit platform implementations. There is still similar work to do with apps and submodules names to clean in mnit, but it will be for a future PR.

Pull-Request: #1671
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>

diff --combined lib/sdl.nit
index 04d9fac,a8fa112..ed60975
--- 1/lib/sdl.nit
--- 2/lib/sdl.nit
+++ b/lib/sdl.nit
@@@ -14,13 -14,13 +14,13 @@@
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
- # SDL display support (used in Linux for windows and inputes only)
+ # Simple DirectMedia Layer
  module sdl is
        cflags exec("sdl-config", "--cflags")
        ldflags(exec("sdl-config", "--libs"), "-lSDL_image -lSDL_ttf")
  end
  
 -import mnit_display
 +import mnit::display
  import c
  
  in "C header" `{
@@@ -77,15 -77,15 +77,15 @@@ extern class SDLDisplay `{SDL_Surface *
                SDL_FillRect(self, NULL, SDL_MapRGB(self->format,r,g,b));
        `}
  
-       redef fun width: Int `{ return self->w; `}
-       redef fun height: Int `{ return self->h; `}
+       redef fun width `{ return self->w; `}
+       redef fun height `{ return self->h; `}
  
        # Fill a rectangle with given color
        fun fill_rect(rect: SDLRectangle, r, g, b: Int) `{
                SDL_FillRect(self, rect,  SDL_MapRGB(self->format,r,g,b));
        `}
  
-       redef fun clear(r, g, b: Float) `{
+       redef fun clear(r, g, b) `{
                Uint8 ri, gi, bi;
                ri = (Uint8)r*255;
                gi = (Uint8)g*255;
@@@ -247,8 -247,8 +247,8 @@@ extern class SDLImag
        # Destroy the image and free the memory
        redef fun destroy `{ SDL_FreeSurface(self); `}
  
-       redef fun width: Int `{ return self->w; `}
-       redef fun height: Int `{ return self->h; `}
+       redef fun width `{ return self->w; `}
+       redef fun height `{ return self->h; `}
  
        fun is_ok: Bool do return not address_is_null
  
@@@ -309,8 -309,8 +309,8 @@@ class SDLMouseButtonEven
  
        var button: Int
  
-       redef var pressed: Bool
-       redef fun depressed: Bool do return not pressed
+       redef var pressed
+       redef fun depressed do return not pressed
  
        # Is this event raised by the left button?
        fun is_left_button: Bool do return button == 1
@@@ -355,8 -355,8 +355,8 @@@ class SDLMouseMotionEven
        var rel_x: Float
        var rel_y: Float
  
-       redef var pressed: Bool
-       redef fun depressed: Bool do return not pressed
+       redef var pressed
+       redef fun depressed do return not pressed
  
        init (x, y, rel_x, rel_y: Float, pressed: Bool)
        do
@@@ -384,7 -384,7 +384,7 @@@ class SDLKeyEven
                self.down = down
        end
  
-       redef fun to_c: nullable Char
+       redef fun to_c
        do
                if name.length == 1 then return name.chars.first
                return null