Add ALPN support based on PR #64 from xnyhps

samples/alpn/client.lua

@@ -0,0 +1,27 @@
+--
+-- Public domain
+--
+local socket = require("socket")
+local ssl    = require("ssl")
+
+local params = {
+   mode = "client",
+   protocol = "tlsv1_2",
+   key = "../certs/clientAkey.pem",
+   certificate = "../certs/clientA.pem",
+   cafile = "../certs/rootA.pem",
+   verify = {"peer", "fail_if_no_peer_cert"},
+   options = "all",
+   --alpn = {"foo","bar","baz"}
+   alpn = "foo"
+}
+
+local peer = socket.tcp()
+peer:connect("127.0.0.1", 8888)
+
+peer = assert( ssl.wrap(peer, params) )
+assert(peer:dohandshake())
+
+print("ALPN", peer:getalpn())
+
+peer:close()