message: Hook up back and forward buttons.
diff: @@ -11,14 +11,15 @@ export function mkCommandUri(commandName: string, ...args: any): string {
  export class DocViewProvider implements Disposable {
  private subscriptions: Disposable[] = [];
  - private currentHtml : string = "";
  + private currentHtml: string = '';
  private backstack: string[] = [];
  private forwardstack: string[] = [];
  constructor() {
  this.subscriptions.push(
  commands.registerCommand('lean.openDocView', (url) => this.open(url)),
  + commands.registerCommand('lean.backDocView', () => this.back()),
  + commands.registerCommand('lean.forwardDocView', () => this.forward()),
  commands.registerCommand('lean.openTryIt', (code) => this.tryIt(code)),
  - //commands.registerCommand("workbench.action.navigateBack", () => this.back()),
  );
  }
  @@ -72,10 +73,11 @@ export class DocViewProvider implements Disposable {
  link.attribs.href = mkCommandUri('lean.openDocView', href);
  }
  }
  - let button = $('<input type="button" value="back"/>');
  - button.attribs.href = mkCommandUri("lean.backDocView");
  - $("body").prepend(button)
  - if (this.currentHtml) {this.backstack.push(this.currentHtml);}
  + $(`<nav style="box-sizing: border-box; position : sticky; top : 0px; padding : 4px; background : white">
  + <a class="btn" href="${mkCommandUri('lean.backDocView')}">back</a>
  + <a class="btn" href="${mkCommandUri('lean.forwardDocView')}">forward</a>
  + </nav>`).prependTo('body');
  + if (this.currentHtml) {this.backstack.push(this.currentHtml); this.forwardstack = [];}
  this.currentHtml = $.html();
  this.getWebview().webview.html = this.currentHtml;
  }
  