feat: implement whisper, (double)click on avatar

Users can insert a mention by clicking, and initiate a whisper by
double-clicking on the avatar on a user's chat message

src/lib/Input.svelte

@@ -1,11 +1,20 @@
 <script lang="ts">
  import { tick } from "svelte"
- import { send } from "./chat";
+ import { send, whisper } from "./chat";
 
- let input = "";
+ export let input = "";
  async function keydown(e: KeyboardEvent) {
      if(e.key === "Enter") {
-	 send(input);
+	 console.log(e);
+	 const tokens = input.trim().split(" ");
+
+	 if(tokens[0] === '/w') {
+	     const who = tokens[1];
+	     const m = tokens.slice(2).join(' ');
+	     whisper(who, m);
+	 } else {
+	     send(input);
+	 }
 	 e.preventDefault();
 	 await tick();
 	 input = "";