chore: prep version 0.4.0 (#219)

Author: Noah-Kennedy

Cargo.lock

@@ -1,10 +1,11 @@
 [package]
 name = "boringtun"
 description = "an implementation of the WireGuard® protocol designed for portability and speed"
-version = "0.3.0"
-authors = ["Vlad Krasnov <vlad@cloudflare.com>"]
+version = "0.4.0"
+authors = ["Noah Kennedy <[email protected]>", "Andy Grover <agrover@cloudflare.com>"]
 license = "BSD-3-Clause"
 repository = "https://github.com/cloudflare/boringtun"
+documentation = "https://docs.rs/boringtun/0.4.0/boringtun/"
 edition = "2018"
 
 [dependencies]