A KCP implementation in Rust

I use Rust nightly, stable version should work too.

$ make test

# results:
default mode result (27879ms):
avgrtt=3820 maxrtt=7887

normal mode result (20166ms):
avgrtt=144 maxrtt=363

fast mode result (20133ms):
avgrtt=138 maxrtt=339

To test KcpStream, you can run this in one terminal:

cargo run --example echo

and in another terminal you can run:

cargo run --example connect 127.0.0.1:8080

Each line you type in to the connect terminal should be echo'd back to you! If you open up multiple terminals running the connect example you should be able to see them all make progress simultaneously.

• Migrate all tests from C version and fix bugs
• Verify correctness
• Improve the quality of code and make it more Rust-y