Add docuteOptions to pass options into docute

[johnsusek]

This allows more flexibility to add docute options to the output.

Example vuese.config.js:

module.exports = {
  docuteOptions: {
    darkThemeToggler: true
  }
};

Additionally, if docuteOptions.sidebar exists, the sidebars will be merged with the custom content first, then vuese sidebar below it.

In this screenshot, the "Plugins" section is defined like this in the config:

module.exports = {
  docuteOptions: {
    sidebar: [
      {
        title: 'Plugins',
        links: [
          {
            title: 'EvMenu',
            link: '/plugins/EvMenu'
          }
        ]
      }
    ]
  }
};

Thanks!