Add window maximization API

Implement a simple API to set a window to maximized. Implement it
only for the X11 backend.

src/window.rs

@@ -66,6 +66,13 @@ impl WindowBuilder {
         self
     }
 
+    /// Requests maximized mode.
+    #[inline]
+    pub fn with_maximized(mut self, maximized: bool) -> WindowBuilder {
+        self.window.maximized = maximized;
+        self
+    }
+
     /// Sets whether the window will be initially hidden or visible.
     #[inline]
     pub fn with_visibility(mut self, visible: bool) -> WindowBuilder {
@@ -292,6 +299,12 @@ impl Window {
         self.window.set_cursor_state(state)
     }
 
+    /// Sets the window to maximized or back
+    #[inline]
+    pub fn set_maximized(&self, maximized: bool) {
+        self.window.set_maximized(maximized)
+    }
+
     #[inline]
     pub fn id(&self) -> WindowId {
         WindowId(self.window.id())