add kafka.ApiVersion.Format (segmentio#395)

* add kafka.ApiVersion.Format

* set explicit constant values intead of using iota

Updated constant for `FirstOffset` with correct type (segmentio#368)

Closes segmentio#367

ReaderConfig.RetentionTime usage (segmentio#341)

Using RetentionTime from ReaderConfig on create NewConsumerGroup

don't use io.StringWriter (segmentio#337)

Fixed compatibility with the sarama hash partitioner (segmentio#336)

Previously, if the 32 bit hash code had its most significant bit set, kafka-go
and sarama would select different partitions.

Stream compression (segmentio#306)

* implement stream compression

* fix zstd + pass benchmarks

* add comments and remove old API

* add kafka.CompressionCodec.Name()

* avoid a copy when the output buffer for decoding snappy compressed data is large enough

* fix xerial framing + validate against go-xerial-snappy

* remove unused function

* PR feedback

* cleanup APIs + improve benchmarks

* optimize gzip reader

* fix snappy compression codec

* support running decompression benchmarks alone

add kafka.SeekDontCheck (segmentio#295)

* add kafka.SeekDontCheck

* fix logic

* touch less code

* use SeekDontCheck in ReadBatch

* add test

fix record timestamp delta (segmentio#266)

* fix record timestamp delta

* better tests

* fix go vet complains

* truncate timestamp to milliseconds in generated message sequences

Add MaxAttempts to Reader (segmentio#264)

Small fix to Dialer to set the ServerName in tls.Config if it is empt…

…y. (segmentio#152)