added config option to change the transition time

conf.json.example

 {
 	"slides": "exampleSlides",
+	"transition_time": 1,
 	"interval": 5000,
 	"port": 8080
 }

index.html

 	}
 
 	#_overlay {
-		transition: opacity 1s;
+		transition: opacity {{transition_time}}s;
 		opacity: 1;
 	}
 	#_overlay.hidden {
 		<div id="_main" class="_content"></div>
 		<div id="_overlay" class="_content"></div>
 
+		<!-- Fetch polyfill -->
+		<script src="https://cdnjs.cloudflare.com/ajax/libs/fetch/1.0.0/fetch.min.js"></script>
+
 <script>
 	var overlay = () => document.querySelector("#_overlay");
 	var main = () => document.querySelector("#_main");

server.js

 var pathlib = require("path");
 var urllib = require("url");
 
-var index = fs.readFileSync("index.html");
 var conf = JSON.parse(fs.readFileSync("conf.json"));
+var index = fs.readFileSync("index.html", "utf-8")
+	.replace("{{transition_time}}", conf.transition_time);
 
 function error(res, err) {
 	console.trace(err);