Split usb_report_descriptor into usb_hid_{item,usage}

This is cleaner IMO.

* usb_hid_item deals with parsing the report descriptor.
* usb_hid_usage has tables that define each usage.

usb_hid_usage/src/lib.rs

@@ -0,0 +1,63 @@
+//!
+//! ## References
+//!
+//! * <https://www.usb.org/sites/default/files/hut1_3_0.pdf>
+
+#![no_std]
+
+macro_rules! usage {
+    { [$page:literal] $($i:literal $v:ident)* } => {
+        pub const PAGE: u16 = $page;
+
+        #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+        #[non_exhaustive]
+        pub enum Usage {
+            $($v,)*
+        }
+
+        impl TryFrom<u16> for Usage {
+            type Error = super::UnknownUsage;
+
+            fn try_from(n: u16) -> Result<Self, Self::Error> {
+                Ok(match n {
+                    $($i => Self::$v,)*
+                    _ => return Err(super::UnknownUsage),
+                })
+            }
+        }
+    };
+}
+
+macro_rules! page {
+    { $($v:ident $m:ident)* } => {
+        $(pub mod $m;)*
+
+        #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+        #[non_exhaustive]
+        pub enum UsagePage {
+            $($v,)*
+        }
+
+        impl TryFrom<u16> for UsagePage {
+            type Error = UnknownPage;
+
+            fn try_from(n: u16) -> Result<Self, Self::Error> {
+                Ok(match n {
+                    $($m::PAGE => Self::$v,)*
+                    _ => return Err(UnknownPage),
+                })
+            }
+        }
+    };
+}
+
+page! {
+    GenericDesktop generic_desktop
+    Button button
+}
+
+#[derive(Debug)]
+pub struct UnknownUsage;
+
+#[derive(Debug)]
+pub struct UnknownPage;