Minor fixes and documentation

• Remove opengraph and twitter from documentation because they weren't used (thank you @tdharmon)
• Update dependencies and peer dependencies - fixes #48 (thank you @mikelax for the report and @RomanGotsiy for the reminder)

WebApp Manifest Configuration - 3.1.0

This version adds support of WebApp manifest configuration. You just have to add these parameters to the plugin options:

{
    // WebApp Manifest Configuration
    appName: 'Gatsby site',
    appDescription: null,
    developerName: null,
    developerURL: null,
    dir: 'auto',
    lang: 'en-US',
    background: '#fff',
    theme_color: '#fff',
    display: 'standalone',
    orientation: 'any',
    start_url: '/?homescreen=1',
    version: '1.0'
}

title is now deprecated in favor of appName.

Gatsby v2 - 3.0.0

Welcome to Gatsby v2!

This version is a full rewrite of the HTML generator. It uses the markup generated by favicons-webpack-plugin and inserts it in the Gatsby workflow. For now, I removed the option to disable HTML generation from the previous version.

Feel free to report any bug or feature.