TinyTemplate converts the context structure to serde_json::Value internally so that it can look up values by string keys. This introduces a dependency on serde_json even though we don't really do any JSON serialization. If TinyTemplate had its own version of Value which could be constructed by a custom serde serializer, we could drop serde_json and only depend on serde.

This is not a high priority for Criterion.rs (which depends on serde_json anyway). I would be happy to accept a pull request though.