cue: implement regexp support

add support for both unary and binary operators

Change-Id: I6d470b93b38fc30f1b682fcee34229acd7945ea5
diff --git a/cue/ast.go b/cue/ast.go
index 7b067bd..e1303ea 100644
--- a/cue/ast.go
+++ b/cue/ast.go
@@ -464,7 +464,8 @@
 				tokenMap[n.Op],
 				v.walk(n.X),
 			}
-		case token.GEQ, token.GTR, token.LSS, token.LEQ, token.NEQ:
+		case token.GEQ, token.GTR, token.LSS, token.LEQ,
+			token.NEQ, token.MAT, token.NMAT:
 			value = &bound{
 				newExpr(n),
 				tokenMap[n.Op],