This is technically a breaking change because it halves the upper range
of accepted values for byte counts. I thought that fine under the
assumption it will be rare for users to ever want to specify something
in the upper half of `u64`'s value range, especially considering that
this can pave the way for having negative byte offsets (instead of just
counts).
Technically a breaking change for architectures where
`size_of::<usize>() > size_of::<u64>()`, but that strikes me as
extremely unlikely.
This change is important because most file seek offsets, even on older
architectures with word sizes smaller than `u32`, accept a `u64`. In
particular, Rust's own `std` acknowledges this. So, we're actually going
against prior art in Rust by using a `usize`.
This is technically a breaking change, since the data and behavior of
`Input` is exposed publicly. However, it seems unlikely to me that
clients actually depended on a failure in the case that's being changed.
Erich Gubler