search: init Search feature (#105)

* based on https://gist.github.com/cmod/5410eae147e4318164258742dd053993
* modified working for PaperMod
* fetches current lang index.json for search
* add fuse.js v6.4.3 LICENSE: Apache License 2.0
* bundled fastsearch and fusejs as search.js

Co-authored-by: Craig Mod <stuff@craigmod.com>

assets/js/fastsearch.js

@@ -0,0 +1,57 @@
+var fuse; // holds our search engine
+
+// load our search index, only executed onload
+function loadSearch() {
+    var xhr = new XMLHttpRequest();
+    xhr.onreadystatechange = function () {
+        if (xhr.readyState === 4) {
+            if (xhr.status === 200) {
+                var data = JSON.parse(xhr.responseText);
+                if (data) {
+                    // fuse.js options; check fuse.js website for details
+                    var options = {
+                        isCaseSensitive: false,
+                        shouldSort: true,
+                        location: 0,
+                        distance: 100,
+                        threshold: 0.4,
+                        minMatchCharLength: 0,
+                        keys: [
+                            'title',
+                            'permalink',
+                            'summary',
+                            'content'
+                        ]
+                    };
+                    fuse = new Fuse(data, options); // build the index from the json file
+                }
+            } else {
+                console.log(xhr.responseText);
+            }
+        }
+    };
+    xhr.open('GET', "../index.json");
+    xhr.send();
+}
+
+// execute search as each character is typed
+document.getElementById("searchInput").onkeyup = function (e) {
+    // run a search query (for "term") every time a letter is typed
+    // in the search box
+    const results = fuse.search(this.value); // the actual query being run using fuse.js
+
+    if (results.length !== 0) {
+        // build our html if result exists
+        let resultSet = ''; // our results bucket
+
+        for (let item in results) {
+            resultSet = resultSet + itemGen(results[item].item.title, results[item].item.permalink)
+        }
+
+        document.getElementById("searchResults").innerHTML = resultSet;
+    }
+}
+
+function itemGen(name, link) {
+    return `<li class="post-entry"><header class="entry-header">${name}&nbsp;»</header><a href="${link}" aria-label="${name}"></a></li>`
+}