ui: merge package input

Event handling is as fundamental as operations, so move the input
package declarations to package ui.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/doc.go

@@ -80,5 +80,32 @@ size vary between platforms and displays.
 To maintain a constant visual size across platforms and displays, always
 use dps or sps to define user interfaces. Only use pixels for derived
 values.
+
+Events
+
+The Queue interface is the protocol for receiving external events.
+
+For example:
+
+	var queue ui.Queue = ...
+
+	for e, ok := queue.Next(h); ok; e, ok = queue.Next(h) {
+		switch e.(type) {
+			...
+		}
+	}
+
+In general, handlers must be declared before events become
+available. Other packages such as pointer and key provide
+the means for declaring handlers for specific event types.
+
+The following example declares a handler ready for key input:
+
+	import gioui.org/ui/key
+
+	ops := new(ui.Ops)
+	var h *Handler = ...
+	key.InputOp{Key: h}.Add(ops)
+
 */
 package ui