ENH: Add javacript to dynamically populate version chooser

This reads a versions.json from the root of the documentation repository
to determine what versions are available. Set up this json file to be
created during documentation deployment.

ci/deploy_docs.sh

@@ -35,6 +35,10 @@ if [[ "${VERSION}" != "dev" ]]; then
     ln -snf ${VERSION} latest
 fi
 
+# Generate our json list of versions
+echo Generating versions.json...
+${TRAVIS_BUILD_DIR}/ci/gen_versions_json.py
+
 echo Staging...
 git add -A .
 if [[ "${VERSION}" == "dev" && `git log -1 --format='%s'` == *"dev"* ]]; then

ci/gen_versions_json.py

@@ -0,0 +1,11 @@
+#!/usr/bin/env python
+# Copyright (c) 2017 MetPy Developers.
+# Distributed under the terms of the BSD 3-Clause License.
+# SPDX-License-Identifier: BSD-3-Clause
+"""Generate versions.json from directory with different doc versions."""
+
+import glob
+
+with open('versions.json', 'wt') as version_file:
+    version_strings = ','.join('"{}"'.format(d) for d in glob.glob('v*.[0-9]*'))
+    version_file.write('{"versions":["latest","dev",' + version_strings + ']}\n')

docs/_static/pop_ver.js

@@ -0,0 +1,17 @@
+$(document).ready(function() {
+    var proj_end = document.baseURI.indexOf("MetPy") + 6;
+    var end = document.baseURI.indexOf("/", proj_end);
+    var cur_ver = document.baseURI.substring(proj_end, end);
+    var name = cur_ver.startsWith('v') ? cur_ver.substring(1) : cur_ver;
+    var mylist = $("#version-list");
+    mylist.empty();
+    mylist.append($("<option>", {value: "../" + cur_ver, text: name}));
+    $.getJSON("../versions.json", function(obj) {
+        $.each(obj.versions, function() {
+            if (this != cur_ver) {
+                name = this.startsWith('v') ? this.substring(1) : this;
+                mylist.append($("<option>", {value: "../" + this, text: name}));
+            }
+        });
+    });
+});

docs/_templates/footer.html

@@ -1,5 +1,6 @@
 {% extends "!footer.html" %}
 {% block extrafooter %}
+    {{ super() }}
 <script>
   (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
   (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
@@ -8,10 +9,10 @@
 
   ga('create', 'UA-92978945-1', 'auto');
   ga('send', 'pageview');
-
 </script>
+<script type="text/javascript" src="_static/jquery.js"></script>
+<script type="text/javascript" src="_static/pop_ver.js"></script>
 <p>Do you enjoy using MetPy?
   <a href="https://saythanks.io/to/unidata" class="btn btn-neutral" title="Installation Guide" accesskey="n">Say Thanks!</a>
 </p>
-    {{ super() }}
 {% endblock %}