_keypressHandler(e, prompt) {
    // Remove tab characters from user input.
    prompt.rl.line = prompt.rl.line.replace(/\t+/, '');

    // Mask passwords.
    const line = prompt.getType() !== 'password' ?
      prompt.rl.line :
      '*'.repeat(prompt.rl.line.length);

    // Re-write render function.
    const width = prompt.rl.line.length;
    const newWidth = prompt.rl.line.length;
    const diff = newWidth - width;
    prompt.rl.cursor += diff;
    const cursor = 0;
    let message = prompt.getQuestion();
    const addition = (prompt.status === 'answered') ?
      chalk.cyan(prompt.answer) :
      line;
    message += addition;
    prompt.screen.render(message, {cursor: cursor});

    const key = (e.key || {}).name;
    const value = (prompt) ? String(line) : undefined;
    this.emit('vorpal_ui_keypress', {key: key, value: value, e: e});
  }
Event handler for keypresses - deals with command history
and tabbed auto-completion.

@param {Event} e
@param {Prompt} prompt
@api private