Add some reader settings and fix the z-index dodging code

reader.js

@@ -2,6 +2,44 @@
 
 'use strict';
 
+// updated by a timer looping function, based on local storage set by the options page
+// we only use a tiny number of settings here
+
+let settings = {
+reader_reverse: false
+};
+
+async function settings_init()
+{
+    try
+    {
+        async function getvar(name, defval)
+        {
+            let temp = (await browser.storage.local.get(name))[name];
+            if(temp == undefined)
+                temp = defval;
+            settings[name] = temp;
+        }
+        getvar("reader_reverse", false);
+    } catch(err) {} // options not stored yet
+}
+
+settings_init();
+
+browser.storage.onChanged.addListener((updates, storageArea) =>
+{
+    if(storageArea != "local") return;
+    for(let setting of Object.entries(updates))
+    {
+        let option = setting[0];
+        let value = setting[1];
+        if(Object.keys(settings).includes(option))
+            settings[option] = value.newValue;
+    }
+});
+
+// actual reder code
+
 function might_have_japanese(text)
 {
     for(let char of text)
@@ -19,7 +57,10 @@ function update(text)
     let newnode = document.createElement("p");
     newnode.textContent = text;
     
-    target.insertBefore(newnode, document.body.firstChild);
+    if(!settings.reader_reverse)
+        target.insertBefore(newnode, document.body.firstChild);
+    else
+        target.appendChild(newnode);
 }
 
 let text_previous = "";