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
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