C++ std::vector<T> and Rust std::vec::Vec<T> support

Add basic std::vector and std::vec::Vec support across FFI boundary.
diff --git a/syntax/error.rs b/syntax/error.rs
index f52d651..103a54f 100644
--- a/syntax/error.rs
+++ b/syntax/error.rs
@@ -15,6 +15,7 @@
 
 pub static ERRORS: &[Error] = &[
     BOX_CXX_TYPE,
+    VEC_CXX_TYPE,
     CXXBRIDGE_RESERVED,
     CXX_STRING_BY_VALUE,
     CXX_TYPE_BY_VALUE,
@@ -29,6 +30,12 @@
     note: Some("hint: use UniquePtr<>"),
 };
 
+pub static VEC_CXX_TYPE: Error = Error {
+    msg: "Vec of a C++ type is not supported yet",
+    label: None,
+    note: Some("hint: use UniquePtr<>"),
+};
+
 pub static CXXBRIDGE_RESERVED: Error = Error {
     msg: "identifiers starting with cxxbridge are reserved",
     label: Some("reserved identifier"),