clearer login and register errors

see #41

js/register.js

@@ -0,0 +1,37 @@
+async function register() {
+    if(document.getElementById("pass").value.length < 10) {
+        alert("Password has to be at least 10 characters long")
+        return;
+    }
+    if(document.getElementById("user").value.length > 25) {
+        alert("Username is too long!")
+        return;
+    }
+    if(document.getElementById("user").value.search("@") != -1) {
+        alert("User cannot contain '@' character!")
+        return;
+    }
+    let r = (await post("/register",{
+        user: document.getElementById("user").value,
+        pass: document.getElementById("pass").value
+    }))
+    console.log(r)
+    if(!r.url.endsWith("/user?success=true")) {
+        if(r.url.endsWith("already_exists")) {
+            alert("An account with that name already exists! Did you mean to login?")
+            return
+        }
+        //fallback
+        document.getElementById("pass").value = ""
+        console.error("registration failed")
+        alert("Registration failed")
+        return;
+    }
+    window.location = "/user"
+}
+
+function passkeydown(e) {
+    if(e.code == "Enter") {
+        register()
+    }
+}