POC usage of rust-metrics in tokio

Building up towards a metrics solution for integration into tokio.

This crate is a simple http server with two routes. / route simply returns while /slow route performs a sum of 2000000 random i32. Metrics are implemented by wrapping rust-metrics structs with Futures in line with tokio asyncness :).

On each connection current metrics are spit out to stdout:

slow, 1 # number of slow requests executed
open, 0 # number of open connections
fast, 0 # number of fast requests executed

Also incuded is the locustfile that can be used to test performance and accuarcy of metrics implementation.

# run server
cargo run --release

# install and run locust
pip install locustio
locust -f locustfile.py --host=http://127.0.0.1:8080

# go to localhost:8089 and start pounding