Important bug fix for null responses (Jerry Sievert)

Many contributed features and fixes, including:

* Pure JavaScript reply parser that is usually faster than hiredis (Jerry Sievert)
* Remove hiredis as optionalDependency from package.json. It still works if you want it.
* Restore client state on reconnect, including select, subscribe, and monitor. (Ignacio Burgueño)
* Fix idle event (Trae Robrock)
* Many documentation improvements and bug fixes (David Trejo)

Many contributed fixes. Thank you, contributors.

* [redisGH-190] - pub/sub mode fix (Brian Noguchi)
* [redisGH-165] - parser selection fix (TEHEK)
* numerous documentation and examples updates
* auth errors emit Errors instead of Strings (David Trejo)

Fix regression in reconnect logic.

Very much need automated tests for reconnection and queue logic.

Many contributed fixes. Thanks everybody.

* [redisGH-127] - properly re-initialize parser on reconnect
* [redisGH-136] - handle passing undefined as callback (Ian Babrou)
* [redisGH-139] - properly handle exceptions thrown in pub/sub event handlers (Felix Geisendörfer)
* [redisGH-141] - detect closing state on stream error (Felix Geisendörfer)
* [redisGH-142] - re-select database on reconnection (Jean-Hugues Pinson)
* [redisGH-146] - add sort example (Maksim Lin)

Some more goodies:

* Fix bugs with node 0.6
* Performance improvements
* New version of `multi_bench.js` that tests more realistic scenarios
* [redisGH-140] - support optional callback for subscribe commands
* Properly flush and error out command queue when connection fails
* Initial work on reconnection thresholds

Fix and test for [redisGH-123]

Passing an Array as as the last argument should expand as users
expect.  The old behavior was to coerce the arguments into Strings,
which did surprising things with Arrays.

Contributed changes:

*  Support SlowBuffers (Umair Siddique)
*  Add Multi to exports (Louis-Philippe Perron)
*  Fix for drain event calculation (Vladimir Dronnikov)

Thanks!

Bugs fixed:

*  authentication retry while server is loading db (danmaz74) [redisGH-101]
*  command arguments processing issue with arrays

New features:

*  Auto update of new commands from redis.io (Dave Hoover)
*  Performance improvements and backpressure controls.
*  Commands now return the true/false value from the underlying socket write(s).
*  Implement command_queue high water and low water for more better control of queueing.

See `examples/backpressure_drain.js` for more information.

Add support and tests for Redis scripting through EXEC command.

Bug fix for monitor mode.  (forddg)

Auto update of new commands from redis.io (Dave Hoover)

Lots of bugs fixed.

*  connection error did not properly trigger reconnection logic [redisGH-85]
*  client.hmget(key, [val1, val2]) was not expanding properly [redisGH-66]
*  client.quit() while in pub/sub mode would throw an error [redisGH-87]
*  client.multi(['hmset', 'key', {foo: 'bar'}]) fails [redisGH-92]