API for operation with modal dialogs

This extends on PR #1037 
hmmm -- generating the docs locally produces the correct output for me -

 - (String) accept_confirm(text, options = {}, &blk) - (String) accept_confirm(options = {}, &blk)

Execute the block, accepting a confirm.

Overloads:

    - (String) accept_confirm(text, options = {}, &blk)

    Parameters:
        text (String, Regexp) —

        Text or regex to match against the text in the modal. If not provided any prompt modal is matched

Parameters:

    options (Hash) (defaults to: {}) —

    a customizable set of options

Options Hash (options):

    :wait (Numeric) —

    How long to wait for the modal to appear after executing the block.

Returns:

    (String) —

    the message shown in the modal

Raises:

    (Capybara::ModalNotFound) —

    if modal dialog hasn't been found