Add letterSpacing typings and test

fixtures/typings-test/typings-test.ts

@@ -140,6 +140,7 @@ namespace methods_core {
       const r18: (data: string) => void = t.getOption('handler');
       const r19: string = t.getOption('bellSound');
       const r20: string = t.getOption('bellStyle');
+      const r22: number = t.getOption('letterSpacing');
     }
     {
       const t: Terminal = new Terminal();
@@ -157,6 +158,7 @@ namespace methods_core {
       t.setOption('useFlowControl', true);
       t.setOption('visualBell', true);
       t.setOption('colors', ['a', 'b']);
+      t.setOption('letterSpacing', 1);
       t.setOption('cols', 1);
       t.setOption('rows', 1);
       t.setOption('tabStopWidth', 1);

typings/xterm.d.ts

@@ -51,6 +51,11 @@ interface ITerminalOptions {
    */
   fontFamily?: string;
 
+  /**
+   * The spacing in whole pixels between characters..
+   */
+  letterSpacing?: number;
+
   /**
    * The line height used to render text.
    */
@@ -407,7 +412,7 @@ declare module 'xterm' {
      * Retrieves an option's value from the terminal.
      * @param key The option key.
      */
-    getOption(key: 'cols' | 'fontSize' | 'lineHeight' | 'rows' | 'tabStopWidth' | 'scrollback'): number;
+    getOption(key: 'cols' | 'fontSize' | 'letterSpacing' | 'lineHeight' | 'rows' | 'tabStopWidth' | 'scrollback'): number;
     /**
      * Retrieves an option's value from the terminal.
      * @param key The option key.
@@ -459,7 +464,7 @@ declare module 'xterm' {
      * @param key The option key.
      * @param value The option value.
      */
-    setOption(key: 'cols' | 'fontSize' | 'lineHeight' | 'rows' | 'tabStopWidth' | 'scrollback', value: number): void;
+    setOption(key: 'cols' | 'fontSize' | 'letterSpacing' | 'lineHeight' | 'rows' | 'tabStopWidth' | 'scrollback', value: number): void;
     /**
      * Sets an option on the terminal.
      * @param key The option key.