chore(build): use third_party.go

use the third_party.go project to replace our update script. This
requires moving a few things around and gets rid of a few annoying bugs:

- You can now bump individual packages
- A new src directory isn't created on build
- Less shell scripting!
- Things get built into ./bin/

third_party/github.com/gorilla/mux/bench_test.go

@@ -1,21 +0,0 @@
-// Copyright 2012 The Gorilla Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package mux
-
-import (
-	"net/http"
-	"testing"
-)
-
-func BenchmarkMux(b *testing.B) {
-	router := new(Router)
-	handler := func(w http.ResponseWriter, r *http.Request) {}
-	router.HandleFunc("/v1/{v1}", handler)
-
-	request, _ := http.NewRequest("GET", "/v1/anything", nil)
-	for i := 0; i < b.N; i++ {
-		router.ServeHTTP(nil, request)
-	}
-}