Make example runnable as example

Trying to run examples as usual (and as described in the README) fails:

    > cargo run --release --example cosmic
    error: no example target named `cosmic`.

The examples themselves are written as separate crates, and are
therefore not usable as examples (they also won't build via `cargo build
--examples`).

This commit makes the example fit the style that cargo can understand.
That is:

- Don't declare the example as a separate crate.
- Remove the nested `src` inside the example directory.
- Put example-only dependencies in dev-dependencies

No rust code was modified, files were only moved.

examples/cosmic/window/input_devices.rs

@@ -0,0 +1,47 @@
+use super::{Page, SubPage};
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum InputDevicesPage {
+    Keyboard,
+    Touchpad,
+    Mouse,
+}
+
+impl SubPage for InputDevicesPage {
+    //TODO: translate
+    fn title(&self) -> &'static str {
+        use InputDevicesPage::*;
+        match self {
+            Keyboard => "Keyboard",
+            Touchpad => "Touchpad",
+            Mouse => "Mouse",
+        }
+    }
+
+    //TODO: translate
+    fn description(&self) -> &'static str {
+        use InputDevicesPage::*;
+        match self {
+            Keyboard => "Input sources, switching, special character entry, shortcuts.",
+            Touchpad => "Touchpad speed, click options, gestures.",
+            Mouse => "Mouse speed, acceleration, natural scrolling.",
+        }
+    }
+
+    fn icon_name(&self) -> &'static str {
+        use InputDevicesPage::*;
+        match self {
+            Keyboard => "input-keyboard-symbolic",
+            Touchpad => "input-touchpad-symbolic",
+            Mouse => "input-mouse-symbolic",
+        }
+    }
+
+    fn parent_page(&self) -> Page {
+        Page::InputDevices(None)
+    }
+
+    fn into_page(self) -> Page {
+        Page::InputDevices(Some(self))
+    }
+}