Rename getters functions removing 'get_' prefix

Follow the suggested Qt style:

http://doc.qt.nokia.com/qq/qq13-apis.html

It seems to me simpler and easier to read.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/endgame.cpp

@@ -87,7 +87,7 @@ namespace {
     fen += string(1, '0' + int(8 - keyCode.length())) + "/8/8/8/8/8/8/8 w - - 0 10";
 
     // Build a Position out of the fen string and get its material key
-    return Position(fen, false, 0).get_material_key();
+    return Position(fen, false, 0).material_key();
   }
 
 } // namespace