Add generic overloads to overloaded functions in d.ts

If we don't have this then tsc will throw errors when passing strings
to the functions, seems wrong to force casting strings to use the
functions, eg. <'bar'>style

typings/xterm.d.ts

@@ -172,13 +172,19 @@ declare module 'xterm' {
      * @param listener The listener.
      */
     on(type: 'title', listener: (title?: string) => void): void;
+    /**
+     * Registers an event listener.
+     * @param type The type of the event.
+     * @param listener The listener.
+     */
+    on(type: string, listener: (...args: any[]) => void): void;
 
     /**
      * Deregisters an event listener.
      * @param type The type of the event.
      * @param listener The listener.
      */
-    off(type: 'blur' | 'focus' | 'lineFeed' | 'data' | 'key' | 'keypress' | 'keydown' | 'refresh' | 'resize' | 'scroll' | 'title', listener: (...args: any[]) => void): void;
+    off(type: 'blur' | 'focus' | 'lineFeed' | 'data' | 'key' | 'keypress' | 'keydown' | 'refresh' | 'resize' | 'scroll' | 'title' | string, listener: (...args: any[]) => void): void;
 
     /**
      * Resizes the terminal.
@@ -333,6 +339,11 @@ declare module 'xterm' {
      * @param key The option key.
      */
     getOption(key: 'handler'): (data: string) => void;
+    /**
+     * Retrieves an option's value from the terminal.
+     * @param key The option key.
+     */
+    getOption(key: string): any;
 
     /**
      * Sets an option on the terminal.
@@ -382,6 +393,12 @@ declare module 'xterm' {
      * @param value The option value.
      */
     setOption(key: 'handler', value: (data: string) => void): void;
+    /**
+     * Sets an option on the terminal.
+     * @param key The option key.
+     * @param value The option value.
+     */
+    setOption(key: string, value: any): void;
 
     /**
      * Tells the renderer to refresh terminal content between two rows