Vendor dependencies

Let's see how I like this workflow.

vendor/wasm-bindgen-macro/ui-tests/bad-signatures.stderr

@@ -0,0 +1,17 @@
+error: cannot return a borrowed ref with #[wasm_bindgen]
+ --> $DIR/bad-signatures.rs:4:17
+  |
+4 | pub fn foo() -> &u32 {}
+  |                 ^^^^
+
+error: unsupported pattern in #[wasm_bindgen] imported function
+ --> $DIR/bad-signatures.rs:8:12
+  |
+8 |     fn foo(Foo(x): Foo);
+  |            ^^^^^^
+
+error: cannot return references in #[wasm_bindgen] imports yet
+  --> $DIR/bad-signatures.rs:10:17
+   |
+10 |     fn foo() -> &u32;
+   |                 ^^^^