Improve documentation on common module

Signed-off-by: Dom Rodriguez <shymega@shymega.org.uk>

src/common/mod.rs

@@ -1,13 +1,38 @@
 //! Common helpers for `displayz`
 
+/// Height and Width of a Display (`usize`)
 pub type Resolution = (usize, usize);
+
+/// X/Y positions of a display.
 pub type Position = (usize, usize);
 
-pub type Displays = Vec<dyn DisplayOutput>;
+/// `Vec` type of the `Display` struct, exposed on a platform-dependent basis.
+pub type Displays = Vec<crate::Display>;
+
+/// `Vec` type of the `Resolution` type, generally exposing a collection of available resolutions.
+pub type Resolutions = Vec<Resolution>;
 
+/// `DisplayOutput` defines the Trait specification of a platform's `Display`.
+/// A `Display` may contain:
+/// - An EDID.
+/// - State, including if the `Display` is active, primary, or has a fault.
+/// - Other helper methods, returning data stored in-memory state.
 pub trait DisplayOutput {
+    /// Returns a boolean result, if the `Display` is the 'primary display' or not.
     fn is_primary(&self) -> bool;
+    /// Returns a boolean result, if the `Display` is currently active or not.
     fn is_active(&self) -> bool;
+    /// Returns a boolean result, if the `Display` is currently focused or not.
+    /// This is not available on all platforms, in the event it's not, it will *always* return `false`.
+    fn is_focused(&self) -> bool {
+        false
+    }
+    /// Returns the `Position` custom type of the `Display`.
     fn get_position(&self) -> Position;
+    /// Returns the `Resolution` custom type of the `Display`.
     fn get_resolution(&self) -> Resolution;
+    /// Returns the `Resolutions` custom type of the `Display`.
+    fn get_resolutions(&self) -> Resolutions;
+    /// Returns the EDID `&str` of the `Display.
+    fn get_edid(&self) -> &str;
 }