make clean does not fail when doc does not exist

With the previous version, running make clean without make doc first
resulted in an error on rmdir doc.
Revert "PLayer interface definitions"

This reverts commit b1d22441ef16654a849643b78180a5370a1f2c8d.
Revert "Player.mli : Définition des methodes d'interfaçage"

This reverts commit 9715a20c70b589ba01c64462223f5a002c3594af.
fix fieldgenerator doc
Implemented focus & better UIManager

- A widget can now be focused.
- The ingame menu now properly locks movement.
- UIManager is now fully polymorphic (no more coercions yay !).
All menus are now implemented
No more ugly option types in Game.ml

-Removed all option types in Game.ml
-Game is now a function (not a class)
Merging master
Merge pull request #86 from GL-MPRI-2014/gamemenus

Gamemenus
Improved Menus.ml (renaming)
Now with a confirmation popup !

-Added some classes, and a new module Windows
-Added a confirmation pop-up when forfeiting
-Added cool borders on menus and buttons
-All buttons/items are now activated by pressing Space
Merge pull request #87 from GL-MPRI-2014/gamemenus

Gamemenus
Trying to fix buttons...
Movement menu cannot be opened anywhere anymore.
Added .merlin to .gitignore, also updated README.
Documentation has been renamed...
Fix issue #84 on load screen
Added gui images
Using new icons in menus
Merge branch 'master' into settings

Conflicts:
	src/interface/Camera.ml