Fix parse_skipped for parsing zeroes

[orlp]

Fixes #9.

[RoDmitry]

Thank you!

[RoDmitry]

Optimized to:

let len_1 = s.len() - 1;
while i < len_1 && *s.get_safe_unchecked(i) == b'0' {
      i += 1;
}

[orlp]

@RoDmitry Pretty sure the compiler would generate identical code for that.

[RoDmitry]

Sadly, but it's not. And sometimes I am very disappointed in a compiler, because I had to even do this. it's usize, it can't go there, but anyway in assembly there was panic (if I remember correctly).

[RoDmitry]

Also functions with only one line of code, you would think that they're gonna be inlined, but it might not. It would not hurt to actually write #[inline].