Support both python3 and python2 for comparisons.
Support both python3 and python2 for comparisons.

Also add tests for concurrency levels 16 and 32, now that I have a
laptop with four cores and eight threads rather than just two cores.

chris-morgan/rust-http,chris-morgan/rust-http,Shraddha512/rust-http,chris-morgan/rust-http,Shraddha512/rust-http,chris-morgan/rust-http,Shraddha512/rust-http,Shraddha512/rust-http,servo/rust-http,servo/rust-http,Shraddha512/rust-http,servo/rust-http,servo/rust-http