lib/connections: Add KCP support (fixes #804)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3489

vendor/github.com/ccding/go-stun/README.md

@@ -0,0 +1,66 @@
+go-stun
+=======
+
+[![Build Status](https://travis-ci.org/ccding/go-stun.svg?branch=master)]
+(https://travis-ci.org/ccding/go-stun)
+[![License](https://img.shields.io/badge/License-Apache%202.0-red.svg)]
+(https://opensource.org/licenses/Apache-2.0)
+[![GoDoc](https://godoc.org/github.com/ccding/go-stun?status.svg)]
+(http://godoc.org/github.com/ccding/go-stun/stun)
+[![Go Report Card](https://goreportcard.com/badge/github.com/ccding/go-stun)]
+(https://goreportcard.com/report/github.com/ccding/go-stun)
+
+go-stun is a STUN (RFC 3489, 5389) client implementation in golang
+(a.k.a. UDP hole punching).
+
+[RFC 3489](https://tools.ietf.org/html/rfc3489):
+STUN - Simple Traversal of User Datagram Protocol (UDP)
+Through Network Address Translators (NATs)
+
+[RFC 5389](https://tools.ietf.org/html/rfc5389):
+Session Traversal Utilities for NAT (STUN)
+
+### Use the Command Line Tool
+
+Simply run these commands (if you have installed golang and set `$GOPATH`)
+```
+go get github.com/ccding/go-stun
+go-stun
+```
+or clone this repo and run these commands
+```
+go build
+./go-stun
+```
+You will get the output like
+```
+NAT Type: Full cone NAT
+External IP Family: 1
+External IP: 166.111.4.100
+External Port: 23009
+```
+You can use `-s` flag to use another STUN server, and use `-v` to work on
+verbose mode.
+```bash
+> ./go-stun --help
+Usage of ./go-stun:
+  -s string
+        server address (default "stun1.l.google.com:19302")
+  -v    verbose mode
+```
+
+### Use the Library
+
+The library `github.com/ccding/go-stun/stun` is extremely easy to use -- just
+one line of code.
+
+```go
+import "github.com/ccding/go-stun/stun"
+
+func main() {
+	nat, host, err := stun.NewClient().Discover()
+}
+```
+
+More details please go to `main.go` and [GoDoc]
+(http://godoc.org/github.com/ccding/go-stun/stun)