Extend Settings API support

[GlennM]

Hello Daniel,

I appreciate the work you've done on creating this plugin template. I'm trying to create a plugin based on it, but discovered the following.

Maybe it's an idea to extend your plugin template with more option types? At this time, it is limited to input fields (strings), ints and radio buttons. So for example dropdown lists are not included, as wel as (multiple) checkboxes.

I've found a plugin which includes this very nice (also take a look at the section navigation tabs at the top). The plugin can be found on https://github.com/tareq1988/wordpress-settings-api-class.

Any ideas to extend the plugin to support more option types? Or to include this "class.settings-api.php" with your plugin?

Thank you in advance!

Glenn

[convissor]

Pull requests following this plugin's existing coding style are always welcome.