Using custom memory allocator (sn_malloc or mimalloc) in FrameworkBenchmark for Drogon

I see Rust based frameworks [actix](https://github.com/TechEmpower/FrameworkBenchmarks/blob/master/frameworks/Rust/actix/src/main_pg.rs#L2) and [may_minhttp](https://github.com/TechEmpower/FrameworkBenchmarks/blob/master/frameworks/Rust/may-minihttp/src/main.rs#L2) both using `sn_malloc` and `mimalloc` allocator which shows significant improvement. Have you tried including custom allocator for Drogon benchmarks?