io/pointer: [API] make cursor name into a byte

Add most of the common cursors defined by different systems.

Normalize cursor names to match CSS.

This is API change: some cursor names have changed, and the
underlying type is no longer a string.

Signed-off-by: Egon Elbre <egonelbre@gmail.com>

io/router/router.go

@@ -298,7 +298,7 @@ func (q *Router) collect() {
 			}
 			pc.inputOp(op, &q.handlers)
 		case ops.TypeCursor:
-			name := encOp.Refs[0].(pointer.CursorName)
+			name := pointer.CursorName(encOp.Data[1])
 			pc.cursor(name)
 		case ops.TypeSource:
 			op := transfer.SourceOp{