Extend functionality to users, post_author, and options repeater

[imantsk]

With my small improvement, now you can also get repeaters from specific users (by ID), form current post_author and form an options page.

Use cases:

• Specific user by ID nr. :: repeater_user_{ID}_{name_of_the_repeater}
• Author of the current post :: repeater_author_{name_of_the_repeater}
• Options page :: repeater_option_{name_of_the_repeater}