all: rename io/event.Key to Tag

Key had an unfortunate association with keyboard input.

This is an API change. The following rewrites were run to fixup
Gio code:

        $ gofmt -r 'pointer.InputOp{Key:a} -> pointer.InputOp{Tag:a}' -w .
        $ gofmt -r 'pointer.InputOp{Key:a, Grab:b} -> pointer.InputOp{Tag:a, Grab:b}' -w .
        $ gofmt -r 'key.InputOp{Key:a} -> key.InputOp{Tag:a}' -w .
        $ gofmt -r 'key.InputOp{Key:a, Focus:b} -> key.InputOp{Tag:a, Focus:b}' -w .
        $ gofmt -r 'event.Key -> event.Tag' -w .

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

io/profile/profile.go

@@ -13,7 +13,7 @@ import (
 // Op registers a handler for receiving
 // Events.
 type Op struct {
-	Key event.Key
+	Tag event.Tag
 }
 
 // Event contains profile data from a single
@@ -24,7 +24,7 @@ type Event struct {
 }
 
 func (p Op) Add(o *op.Ops) {
-	data := o.Write(opconst.TypeProfileLen, p.Key)
+	data := o.Write(opconst.TypeProfileLen, p.Tag)
 	data[0] = byte(opconst.TypeProfile)
 }