Add xterm itegration

* Move to TypeScript from legacy JavaScript
* Add support of xterm.js
* Hterm is still available for backward compatibility

js/dist/websocket.d.ts

@@ -0,0 +1,17 @@
+export declare class ConnectionFactory {
+    url: string;
+    protocols: string[];
+    constructor(url: string, protocols: string[]);
+    create(): Connection;
+}
+export declare class Connection {
+    bare: WebSocket;
+    constructor(url: string, protocols: string[]);
+    open(): void;
+    close(): void;
+    send(data: string): void;
+    isOpen(): boolean;
+    onOpen(callback: () => void): void;
+    onReceive(callback: (data: string) => void): void;
+    onClose(callback: () => void): void;
+}