Create directories for docjar, srcjar and jar targets

Change-Id: I1c5523e0014c781bee41180f42b66da715d18bde
Reviewed-on: http://review.couchbase.org/25329
Tested-by: Deepti Dawar <deepti.dawar@globallogic.com>
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Replaced internal log implementation with slf4j

slf4j allows clients to choose the log implementations that works best for their
needs (logback, log4j, jdk14, avsl, commons-logging, etc).

Less code to mantain in spymemcached codebase :)