Pipelined add/cas/set and misc fixes

• Add support for pipelined ADD/CAS/SET operations.
• Other minor fixes and adjustments.

fix bug in binary mget response

Merge pull request #18 from AdRoll/mget_bugfix

fix bug in binary mget response

support elasticache autodiscovery

Support config values of the form:

{cluster_name, [{servers, {elasticache, ConfigHost, ConfigPort}}]}

when using elasticache (or a node supporting the text command "config get cluster").

CAS, MINCREMENT, and MDELETE

• Add mero:mdelete/3, which supports deleting multiple keys using the same socket (#13).
• Add mero:mincrement_counter/{2,7}, which support incrementing multiple keys (#13).
• Add mero:cas/6, mero:gets/{2,3}, mero:mgets/{2,3}, which support using the check-and-set operation (#14).

Speed Up Socket Creation

This release causes mero to create sockets more rapidly. This is important for high-load systems.

Better parallel GETs

Merge pull request #10 from AdRoll/multiget_in_parallel

Ads support to run parallel multigets both in binary and text protoco…