Adding buffa to rust_serialization_benchmark

[jlucaso1]

Just to raise awareness, I opened a PR for rust_serialization_benchmark adding buffa as another candidate.

Feel free to make suggestions or close this issue as well. djkoloski/rust_serialization_benchmark#142

[iainmcgin]

Very cool, thanks for doing this! I see there was some discussion about the structure of the code - if there's any feedback on API structure, things we can do to improve ergonomics etc, please let me know.