Fix: Small fix for location hash/fragment

[BToersche]

The current location hash implementation will replace all # chars in the fragment, which shouldn't be the case.
While, according to spec, # is not allowed in the fragment portion of the URL, browsers tend to be lenient towards enforcing this. Opening a URL in your browser (be it Chrome or Firefox) with # in the fragment will get accepted and returned in your location hash.

Consider https://github.com/leptos-rs/leptos/#test#bar. Your location hash will return (in Javascript) #test#bar.
The current implementation in Leptos will return testbar while the new implementation will return test#bar, which fits the docs better of the function:

/// Current [`window.location.hash`](https://developer.mozilla.org/en-US/docs/Web/API/Window/location)
/// without the beginning #.

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A small side-note: I've contemplated simply always removing the first char of the fragment (since this should always be # anyways). Like so: if s.is_empty() { s } else { s[1..].to_string() }. I've decided against it, but if you (the reviewer) prefers this implementation, please let me know and I'll update it.

[benwis]

Hi! Your solution seems fine, if a bit verbose.

[benwis]

Thanks for fixing this!