lib8: drop custom RGB8 struct for rgb crate

src/power.rs

@@ -1,7 +1,24 @@
+use rgb::RGB8;
+
 pub trait AsMilliwatts {
     fn as_milliwatts(&self) -> u32;
 }
 
+impl AsMilliwatts for RGB8 {
+    fn as_milliwatts(&self) -> u32 {
+        const RED_MW : u32   = 16 * 5; //< 16mA @ 5v = 80mW
+        const GREEN_MW : u32 = 11 * 5; //< 11mA @ 5v = 55mW
+        const BLUE_MW : u32  = 15 * 5; //< 15mA @ 5v = 75mW
+        const DARK_MW : u32  =  1 * 5; //<  1mA @ 5v =  5mW
+
+        let red = (self.r as u32 * RED_MW).wrapping_shr(8);
+        let green = (self.g as u32 * GREEN_MW).wrapping_shr(8);
+        let blue = (self.b as u32 * BLUE_MW).wrapping_shr(8);
+
+        return red + green + blue + DARK_MW;
+    }
+}
+
 pub fn brightness_for_mw(total_mw : u32, target : u8, max_power: u32) -> u8 {
     let target32 = target as u32;
     let requested_mw = (total_mw * target32) / 256;