Add support for shortcodes

[gytisrepecka]

Add support for shortcodes in the same manner as filters and actions currently existing on boilerplate.

Also included example function (plugin_name_shortcode_func) that can accept shortcode with arguments:

[plugin-name-shortcode argm='123']

[puremana]

Works great, thanks!

[gytisrepecka]

Any chances to merge into master?

[smileBeda]

Great idea, used with a few changes in the new fork of this plugin which will actively take PRs.

Current changes are in develop branch.

Thanks @gytisrepecka