Changed it to remove one of the whiches.

#3
#1

I probably shouldn't have coupled these together in a single commit, but
for some reason I see them as releated.

Chunk splitting support is added in `QuerySpec` as the `Split` and
`ReSplit` fields. Validation is done and tested, but no implementation
is done.

Progress transparency is added in the `Stats` structure as the four
new fields prefixed with `Range`. I thought about various ways of
indicating progress but since conceptually each query represents a scan
across a continguous time range, using `time.Duration` seemed to make
the most sense in the end. Also because it makes just as much sense
for `QueryManager` as for `Stream`.

#3

The previous edition was too complicated, and consequently not very
user-friendly. If you're trying to query some logs, the last thing you
want to do is have to configure two separate parameters based on powers
of two and summing. The last straw for me was I couldn't imagine how one
could expose both of these parameters in a comprehensible way to users
of a command line interface.

Apart from this API rewrite, this commit also fixes an issue with the
Chunk validation where it failed to prevent sub-second granularities in
chunks, which could theoretically cause odd bugs.

#10

#3

It is possible for all data to be read from the stream before the end of
stream chunk is logged as finished.

#1

#3