There are a few aspects of kadm that I'm not 100% happy with,
particularly `NewClient` and `NewOptClient`, but these are a bit wider
used so I'm not going to break them now. We can save these for a v2.0.

I just did a few API breakages, particularly:

- removal of all Into functions, replaced with Offsets or KOffsets
- ListInternalTopics => ListTopicsWithInternal
- MetadataWithoutTopics => BrokerMetadata

These were ugly warts that weren't used much.

I'm sure there are some things that could be a bit better, but nothing
that stands out as needing an obvious fix, and I'm mostly out of ideas
for what to do here.

So, it's time to stabilize this package. This package will likely see
minor releases when adding support for Kafka requests, and potentially a
major release if Kafka adds something or changes something in the
protocol that would warrant a full on change here.

We keep this separate from the main franz-go package, similar to kmsg,
because this is basically supposed to be kmsg but usable, and we want to
have more freedom to make more frequent API changes.