[Navbar] Fix navbar hide on scroll behavior, add explicit hide offset

[luksurious]

Closes #90

Basically, I changed the hideOnScroll behavior in such a way that the navbar is only hidden if a certain threshold is reached (i.e. scrollY is farther than the navbar element / sticky offset or configurable parameter hideOffset), and that the navbar is always reappearing if the scrolling is "at the top" even if the tolerance was not reached (taking same threshold as described above).

As a minor thing, I tried to make the options type safer by casting them according to the expected type.

This is a more opinionated change and I am happy to discuss implementation.
(I am using the current version, though, already in an ongoing web project of mine successfully.)

I put this on top of the working 0.10.x branch as otherwise I was not able to properly test it.

[VizuaaLOG]

Thank you for this! I agree with the types as well!