Hint positions which are breakpoint specific

[michaelpwilson]

This fork will allow the change of a hint's position based on the screen size. The default breakpoints variables are specified in hint-variables.scss

Example:

Large screens: .hint--top-lg Medium screens: .hint--bottom-md Small screens: .hint--top-left-sm Extra small screens: .hint--bottom-right-sm

[chinchang]

@michaelpwilson please commit only .scss files in the PR. CSS files will be automatically build at time of merge.