Vendor dependencies

Let's see how I like this workflow.

vendor/syn/src/print.rs

@@ -0,0 +1,16 @@
+use proc_macro2::TokenStream;
+use quote::ToTokens;
+
+pub struct TokensOrDefault<'a, T: 'a>(pub &'a Option<T>);
+
+impl<'a, T> ToTokens for TokensOrDefault<'a, T>
+where
+    T: ToTokens + Default,
+{
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        match self.0 {
+            Some(t) => t.to_tokens(tokens),
+            None => T::default().to_tokens(tokens),
+        }
+    }
+}