Add functions for filtering by title and post type

go/blog/blog.go

		document.title = baseTitle + " (Posts tagged '" + tag + "')";
	}
	function filterTitle(match) {
		var match = match.toLowerCase();
		var articles = document.querySelectorAll("article");
		for (var i = 0; i < articles.length; i++) {
			var article = articles[i];
			var title = article.querySelector("header h1");
			if (title && title.textContent.toLowerCase().match(match)) {
				article.classList.remove("does-not-match");
			} else {
				article.classList.add("does-not-match");
			}
		}
		document.title = baseTitle + " (Posts matching '" + match + "')";
	}
	function filterId(id) {
		var articles = document.querySelectorAll("article");
		for (var i = 0; i < articles.length; i++) {
		document.title = baseTitle + " (Only post id '" + id + "')";
	}
	function filterType(type) {
		var articles = document.querySelectorAll("article");
		for (var i = 0; i < articles.length; i++) {
			var article = articles[i];
			if (article.classList.contains(type)) {
				article.classList.remove("does-not-match");
			} else {
				article.classList.add("does-not-match");
			}
		}
		document.title = baseTitle + " (Only " + type + " posts)";
	}
	function clearFilter() {
		var articles = document.querySelectorAll("article.does-not-match");
		for (var i = 0; i < articles.length; i++) {