Improve per-key LED. Add extra example

- Small fixes to use all keys on GX502

aura/examples/iterate-keys.rs

@@ -0,0 +1,43 @@
+use rog_aura::{AuraDbusWriter, GX502Layout, Key, KeyColourArray, KeyLayout};
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let mut writer = AuraDbusWriter::new()?;
+
+    let mut key_colours = KeyColourArray::new();
+    let layout = GX502Layout::default();
+
+    writer.init_effect()?;
+    let rows = layout.get_rows();
+    loop {
+        for (r, row) in rows.iter().enumerate() {
+            for (k, key) in row.iter().enumerate() {
+                *key_colours.key(*key).0 = 254;
+                // Last key of previous row
+                if k == 0 {
+                    if r == 0 {
+                        let k = &rows[rows.len() - 1][rows[rows.len() - 1].len() - 1];
+                        *key_colours.key(*k).0 = 0;
+                    } else {
+                        let k = &rows[r - 1][rows[r - 1].len() - 1];
+                        *key_colours.key(*k).0 = 0;
+                    }
+                } else {
+                    let k = &rows[r][k - 1];
+                    *key_colours.key(*k).0 = 0;
+                }
+                *key_colours.key(Key::Up).0 = 255;
+                *key_colours.key(Key::Left).0 = 255;
+                *key_colours.key(Key::Right).0 = 255;
+                *key_colours.key(Key::Down).0 = 255;
+
+                *key_colours.key(Key::W).0 = 255;
+                *key_colours.key(Key::A).0 = 255;
+                *key_colours.key(Key::S).0 = 255;
+                *key_colours.key(Key::D).0 = 255;
+
+                writer.write_colour_block(&key_colours)?;
+                std::thread::sleep(std::time::Duration::from_millis(100));
+            }
+        }
+    }
+}