pull latest kcp features, upgrade to edition 2021

Author: zonyitoo

Cargo.toml

@@ -1,13 +1,17 @@
 [package]
 name = "kcp"
-version = "0.4.16"
+version = "0.5.0"
 authors = ["Matrix <[email protected]>", "Y. T. Chung <[email protected]>"]
 description = "Reliable-UDP Library for Rust"
 license = "MIT"
 readme = "README.md"
 keywords = ["kcp", "udp", "reliable", "net"]
 documentation = "https://docs.rs/kcp"
 repository = "https://github.com/Matrix-Zhang/kcp"
+edition = "2021"
+
+[features]
+fastack-conserve = []
 
 [dependencies]
 bytes = "1.0"