Added Waiter.wait_for!()
Added ElementProxy#wait_until_visible and ElementProxy#wait_until_hidden and aliases for the wait_for_ methods.
Forward exception messages in capybara delegations
Reorder test cases to match methods order.
Remove unnecessary namespacing and use of global resolution operator.
Update README.md [ci skip]

Updated for presence and visibility functionality.
tunneling wait_time through wait_for!
wait_for -> wait_until
Merge pull request #86 from appfolio/addWaitForMortar

Added Waiter.wait_until!, ElementProxy#wait_until_visible, ElementProxy#wait_until_hidden