(doc) Add anchors, script copy button, Gitter and GitHub button

docs/input/_Bottom.cshtml

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+<div class="github-button">
+    <a href="https://github.com/cake-contrib/Cake.DocFx" target="_blank"><i class="fa fa-github"></i> GitHub</a>
+</div>
+<script>
+    ((window.gitter = {}).chat = {}).options = {
+        room: 'cake-contrib/Lobby'
+    };
+</script>
+<script src="https://sidecar.gitter.im/dist/sidecar.v1.js" async defer></script>
+
+<script type="text/javascript" src="@Context.GetLink("/assets/js/anchor.min.js")"></script>
+<script type="text/javascript" src="@Context.GetLink("/assets/js/clipboard.min.js")"></script>
+<script type="text/javascript">
+    anchors.options.placement = 'left';
+    anchors.add('#content > h1,h2,h3,h4');
+
+    var snippets = document.querySelectorAll("pre > code");
+    [].forEach.call(snippets, function(snippet) {
+        snippet.insertAdjacentHTML("beforebegin", "<button class='btn-copy' data-clipboard-snippet><img class='clippy' width=13 src='@Context.GetLink("/assets/images/clippy.svg")' alt='Copy to clipboard'></button>");
+    });
+    var clipboardSnippets = new Clipboard('[data-clipboard-snippet]', {
+        target: function(trigger) {
+            return trigger.nextElementSibling;
+        }
+    });
+    clipboardSnippets.on('success', function(e) {
+        e.clearSelection();
+        showTooltip(e.trigger, "Copied!");
+    });
+    clipboardSnippets.on('error', function(e) {
+        showTooltip(e.trigger, fallbackMessage(e.action));
+    });
+    var btns = document.querySelectorAll('.btn-copy');
+    for (var i = 0; i < btns.length; i++) {
+        btns[i].addEventListener('mouseleave', function(e) {
+            e.currentTarget.setAttribute('class', 'btn-copy');
+            e.currentTarget.removeAttribute('aria-label');
+        });
+    }    
+    function showTooltip(elem, msg) {
+        elem.setAttribute('class', 'btn-copy tooltipped tooltipped-s');
+        elem.setAttribute('aria-label', msg);
+    }
+    function fallbackMessage(action) {
+        var actionMsg = '';
+        var actionKey = (action === 'cut' ? 'X' : 'C');
+        if (/iPhone|iPad/i.test(navigator.userAgent)) {
+            actionMsg = 'No support :(';
+        } else if (/Mac/i.test(navigator.userAgent)) {
+            actionMsg = 'Press ⌘-' + actionKey + ' to ' + action;
+        } else {
+            actionMsg = 'Press Ctrl-' + actionKey + ' to ' + action;
+        }
+        return actionMsg;
+    }        
+</script>

docs/input/assets/css/override.less

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+/* Control the margin for bootstrap alert boxes */
+.alert > p {
+    margin-top: 0px;
+}
+
+/* Control the look and feel of the copy box applied to code sections */
+.btn-copy[disabled] .clippy {
+    opacity: .3;
+}
+pre .btn-copy {
+    -webkit-transition: opacity 0.3s ease-in-out;
+    -o-transition: opacity 0.3s ease-in-out;
+    transition: opacity 0.3s ease-in-out;
+    opacity: 0;
+    padding: 2px 6px;
+    float: right;
+}
+pre:hover .btn-copy {
+    opacity: 1;
+}
+.tooltipped {
+    position: relative
+}
+.tooltipped:after {
+    position: absolute;
+    z-index: 1000000;
+    display: none;
+    padding: 5px 8px;
+    font: normal normal 11px/1.5 Helvetica, arial, nimbussansl, liberationsans, freesans, clean, sans-serif, "Segoe UI Emoji", "Segoe UI Symbol";
+    color: #fff;
+    text-align: center;
+    text-decoration: none;
+    text-shadow: none;
+    text-transform: none;
+    letter-spacing: normal;
+    word-wrap: break-word;
+    white-space: pre;
+    pointer-events: none;
+    content: attr(aria-label);
+    background: rgba(0, 0, 0, 0.8);
+    border-radius: 3px;
+    -webkit-font-smoothing: subpixel-antialiased
+}
+.tooltipped:before {
+    position: absolute;
+    z-index: 1000001;
+    display: none;
+    width: 0;
+    height: 0;
+    color: rgba(0, 0, 0, 0.8);
+    pointer-events: none;
+    content: "";
+    border: 5px solid transparent
+}
+.tooltipped:hover:before, .tooltipped:hover:after, .tooltipped:active:before, .tooltipped:active:after, .tooltipped:focus:before, .tooltipped:focus:after {
+    display: inline-block;
+    text-decoration: none
+}
+.tooltipped-s:after, .tooltipped-se:after, .tooltipped-sw:after {
+    top: 100%;
+    right: 50%;
+    margin-top: 5px
+}
+.tooltipped-s:before, .tooltipped-se:before, .tooltipped-sw:before {
+    top: auto;
+    right: 50%;
+    bottom: -5px;
+    margin-right: -5px;
+    border-bottom-color: rgba(0, 0, 0, 0.8)
+}
+
+@font-family-sans-serif:  "Roboto", Helvetica, Arial, sans-serif;
+
+/* For Gitter and GitHub */
+.bottom-footer {
+	margin-bottom: 40px !important;  // Make room for Gitter and GitHub buttons
+}
+
+.gitter-open-chat-button {
+	background-color: #3c8dbc;
+	font-family: @font-family-sans-serif;
+	letter-spacing: normal;
+	right: 90px;
+}
+
+.gitter-open-chat-button:focus, .gitter-open-chat-button:hover,
+.github-button:focus, .github-button:hover,
+{	
+	background-color: #4EABDD;
+	color: #fff;
+}
+
+.gitter-chat-embed {
+	top: 49px;
+	border-top: 1px solid #000;
+	z-index: 10000;
+}
+
+.github-button {
+	z-index: 100;
+	position: fixed;
+	bottom: 0px;
+	right: 240px;
+	padding: 1em 3em;
+	background-color: #367fa9;
+	border: 0;
+	border-top-left-radius: 0.5em;
+	border-top-right-radius: 0.5em;
+	font-family: sans-serif;
+	font-size: 9pt;
+	text-transform: uppercase;
+	text-align: center;
+	text-decoration: none;
+	cursor: pointer;
+	cursor: hand;
+	-webkit-transition: all .3s ease;
+	transition: all .3s ease;
+	color: #fff;
+	a, a:active, a:hover, a:focus {
+		color: #fff;
+	}
+}