io/pointer: [API] rename PointerEvent.Type to Kind

Kind is the idiomatic field name for distinguishing a struct without
using separate types.

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

io/pointer/pointer_test.go

@@ -8,7 +8,7 @@ import (
 
 func TestTypeString(t *testing.T) {
 	for _, tc := range []struct {
-		typ Type
+		typ Kind
 		res string
 	}{
 		{Cancel, "Cancel"},