Fixes jam1garner#291.

Fixes #291.

(cherry picked from commit 38b3598)

This change adds support for the missing SeekFrom operations. It
refactors the internals a bit. We now keep a range of start..end values
that are accessible to the TakeSeek. I dropped manually computed stream
position and instead call the inner's `stream_position()`. This does
mean that `limit` needs to take in a `&mut`. I was also going to change
the return type to `Result<u64>`, but that would force all callers to
handle the `Result`, which I felt like it was a bigger API change.

I fixed the test added in 38b3598
because `StartFrom::Start(0)` used to reset the cursor to the start of
the underlying buffer.

Fixes jam1garner#291.

The purpose of `TakeSeek` is to be a binrw-compatible version of
`std::io::Take`, and the purpose of `std::io::Take` is only to
truncate the stream to a certain number of bytes, not to extend the
stream if a limit beyond the length of the inner stream is given.
Thus, `TakeSeek` also needs to pay attention to the true end of the
inner stream and use that as the `SeekFrom::End(0)` position if it
is less than the limit.

Refs jam1garner#291.

The purpose of `TakeSeek` is to be a binrw-compatible version of
`std::io::Take`, and the purpose of `std::io::Take` is only to
truncate the stream to a certain number of bytes, not to extend the
stream if a limit beyond the length of the inner stream is given.
Thus, `TakeSeek` also needs to pay attention to the true end of the
inner stream and use that as the `SeekFrom::End(0)` position if it
is less than the limit.

Refs jam1garner#291.

The purpose of `TakeSeek` is to be a binrw-compatible version of
`std::io::Take`, and the purpose of `std::io::Take` is only to
truncate the stream to a certain number of bytes, not to extend the
stream if a limit beyond the length of the inner stream is given.
Thus, `TakeSeek` also needs to pay attention to the true end of the
inner stream and use that as the `SeekFrom::End(0)` position if it
is less than the limit.

Refs jam1garner#291.