Unversion dist folder and generate in prepare (#48)

* Unversion dist folder and generate in prepare

Rather than including build time generated source files in the
repository, use the npm prepare step to create the dist folder
contents after local install and before publishing.

* Switch to suggesting jsdelivr/npm in README

Author: bz2

.gitignore

@@ -1 +1,2 @@
-node_modules
+dist/
+node_modules/

README.md

@@ -32,7 +32,7 @@ Add this line in your HTML code, before `</head>` and replace `<my-api-key>` and
 
 ```HTML
 <!-- Warning: This is an experimental library, do not use it on production environments -->
-<script defer src="https://cdn.jsdelivr.net/gh/GoogleCloudPlatform/stackdriver-errors-js@v0.4.0/dist/stackdriver-errors-concat.min.js"></script>
+<script defer src="https://cdn.jsdelivr.net/npm/stackdriver-errors-js@0.5.0/dist/stackdriver-errors-concat.min.js"></script>
 <script type="text/javascript">
 window.addEventListener('DOMContentLoaded', function() {
   var errorHandler = new StackdriverErrorReporter();