v1.4.2: fix long-standing consumer fetch session bug & EndBeginTxn

This fixes a long standing consumer fetch session issue, and has further
fixes to the v1.4 new EndAndBeginTransaction API, and one very rare data
race.

v1.4.1: fix a miscompilation due to bumping kmsg; other small things

kmsg is now pinned to a stable major version, meaning future changes
should not affect any users. This also fixes a few small issues, bumps
deps, and has a few other small changes.

kmsg: update before v1.0.0

v1.4.0: a feature filled release with some behavior changes

The behavior changes will not affect any current code. Some of the
features can help make user code simpler, some of the features can help
very long lived clients. See the changelog for more details.

v1.3.5: patch release for a panic & three helping behavior changes

v1.3.4: small additional bugfix for twmb#98

The original patch for twmb#98 was not complete, and the lack of
completeness was found while developing a new feature that will shortly
be released in v1.4.

But, to allow people not to upgrade to v1.4, this bugfix has been
backported to v1.3.

See the changelog for more details.

v1.3.3: two minor bug fixes and a few behavior changes

One bug fix is rare and likely has zero impact,
the other bug fix does not result in any erroneous behavior but is good
to fix.

More details, as well as descriptions on the behavior changes, in the
changelog.

v1.3.2: patch unknown-severity bug related to transactions

Because it is difficult to reason about the severity of this bug, if you
use transactions, it is recommended to upgrade to this patch release
immediately.

v1.3.1: one small bugfix, one config validation

This removes a goroutine leak when consuming if a fetch is buffered
after client.Close. For cases where you use one client in your
application and only close the client on program shutdown, this
goroutine leak is inconsequential. If you recreate consuming clients
often, this leak may eventually result in unnecessary memory
consumption.

v1.3.0: three new features, some behavior changes, minor bugfix

This feature release contains three new features (two new APIs: Ping and
an option), a few small behavior changes, and a minor bugfix.