Vendor dependencies for 0.3.0 release

vendor/regex-syntax/src/either.rs

@@ -0,0 +1,8 @@
+/// A simple binary sum type.
+///
+/// This is occasionally useful in an ad hoc fashion.
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum Either<Left, Right> {
+    Left(Left),
+    Right(Right),
+}