SRANDMEMBER optional COUNT argument

Adds support for the new COUNT argument to SRANDMEMBER.  If called
without a count, we will still return a string response (with one
randome member from the set, or false on a failure/type error).

If the count argument is passed, we return instead an array up to
the number asked for, given how Redis will process this value.

http://redis.io/commands/srandmember
Fix formatting issue, remove unneccisary variable
Changed the way we build the HMSET command such that we don't
continue to destroy and reallocate the command buffer

Added a simply library routine to append to a command buffer
using a smart_str

Made the unit tests work even if you're not compiled with
igbinary

Addresses issue #287
Add include for smart_str
Update debian.control

Updated version in debian.control
Merge pull request #289 from goodsoft/patch-1

Updated version in debian.control
Merge remote-tracking branch 'origin/hmset_performance'
Update documentation to new format for our count argument
Fix markdown formatting
Pulling README.markdown from master
Merge branch 'srandmember_count'

Conflicts:
	tests/TestRedis.php
Add prefix support to SUBSCRIBE/PSUBSCRIBE

Now the Redis::OPT_PREFIX will apply to subscribe/psubscribe
channels and will be applied before searching for messages.