Add zstd support

[pikrzysztof]

zstd is supported natively as of kafka 2.1. zstd bindings are available here. I'm not sure about the license though.

It would be great to have it supported by this library.

[zmstone]

I have been a bit slow on following kafka changes.
Latest verified kafka version in this repo's tests is 1.1.

Although we have a snappy lib here,
I am reluctant pulling in another dependency to this repo,
since zstd as well as lz4 are optional.

I prefer to have compression backend configurable.

e.g. we can do:

zstd_decompress(BinData) ->
  {ok, Module} = application:get_env(kafka_protocol, zstd_compression_module),
  Module:decompress(BinData).
zstd_compress(IoData) ->
  {ok, Module} = application:get_env(kafka_protocol, zstd_compression_module),
  Module:compress(IoData).

Or to resolve at compile time, we can override erl_opts with
{d, 'KAFKA_PROTOCOL_ZSTD_MODULE', the_zstd_module} in addition:

-ifdef(KAFKA_PROTOCOL_ZSTD_MODULE).
zstd_decompress(BinData) ->
  ?KAFKA_PROTOCOL_ZSTD_MODULE:decompress(BinData).
zstd_compress(IoData) ->
  ?KAFKA_PROTOCOL_ZSTD_MODULE:compress(IoData).
-else.
zstd_decompress(_BinData) -> error(no_support).
zstd_compress(_IoData) -> error(no_support).
-endif

Then the dependency is put to user's project and we do not have to worry about licensing either.

[bucko909]

I think either of those is likely acceptable. The second solution is probably the most performant as it doesn't have to round-trip ets.