Add tooltip and create hugo shortcode

layouts/shortcodes/git-heatmap.html

@@ -0,0 +1,36 @@
+{{ $js := resources.Get "js/build_heatmap.js" }}
+{{ $p := .Site.Params.heatmap }}
+
+<style>
+:root {
+  --color-empty: {{ $p.color_empty }};
+  --color-low:   {{ $p.color_low }};
+  --color-mid:   {{ $p.color_mid }};
+  --color-high:  {{ $p.color_high }};
+}
+#heatmap text { font-family: inherit; }
+#tooltip {
+  position: fixed;
+  background: #333;
+  color: white;
+  padding: 5px 10px;
+  border-radius: 4px;
+  font-size: 12px;
+  pointer-events: none;
+}
+.hidden { display: none; }
+</style>
+
+<div id="heatmap"></div>
+<script type="module">
+    import {flattenData, constructWeeks, render, setupTooltips} from "{{ $js.RelPermalink }}"
+
+    const data = await fetch("/activity.json").then((r) => r.json());
+    const counts = flattenData(data);
+    const weeks = constructWeeks();
+    const svg = render(weeks, counts);
+    document.getElementById("heatmap").appendChild(svg);
+    setupTooltips(svg);
+</script>
+<div id="tooltip" class="hidden"></div>
+<div id="legend"></div>