Vendor dependencies

Let's see how I like this workflow.

vendor/syn/tests/test_parse_stream.rs

@@ -0,0 +1,12 @@
+use syn::ext::IdentExt;
+use syn::parse::ParseStream;
+use syn::{Ident, Token};
+
+#[test]
+fn test_peek() {
+    _ = |input: ParseStream| {
+        _ = input.peek(Ident);
+        _ = input.peek(Ident::peek_any);
+        _ = input.peek(Token![::]);
+    };
+}