simplify Clear() in Window and its derivatives

it removes argument responsible for immediate refreshing.
since after all calls that were refreshing screen there was
call to Refresh() anyway, this switch doesn't make much sense.

src/window.h

@@ -343,9 +343,8 @@ namespace NCurses
 			virtual void Resize(size_t new_width, size_t new_height);
 			
 			/// Cleares the window
-			/// @param refresh indicates whether window has to be refreshed immediately or not
 			///
-			virtual void Clear(bool refresh = 1);
+			virtual void Clear();
 			
 			/// Adds given file descriptor to the list that will be polled in
 			/// ReadKey() along with stdin and callback that will be invoked