Take top distance into account when hideOnBoundaryHit is false

[danielfdsilva]

Addresses issue https://github.com/gm0t/react-sticky-el/issues/67 Also adds documentation and a story example about the clip-path option.

@gm0t Let me know what you think.

[gm0t]

@danielfdsilva argh... I completely forgot to publish your changes :( Fixing it now, your change is available in 2.0.7 version