Improve benchmark tests (#8)

Simplify the seek logic even further

Rename MaxBehind to MaxLag, speed up a slow test

Batch write/read API (#1)

* Batch write/read API

* readAvailable()

* Improve README and comments

Implement .Close() method to finish the stream

Implement .Skip() for subscriber reconnection logic

Implement subscriber tailing vs. starting behind

Rename .Error() to .Err() to follow stdlib convention

Writer: Remove unnecessary lock when broadcasting by @marino39

Improves throughput 2x.

Kudos to Marcin Gorzynski (https://github.com/marino39) for pointing this out.