docs: add building client library doc
Merge pull request #172 from mreiferson/client_lib_doc_172

docs: building client libraries
nsqd: diskqueue empty removes *all* files

* always try to make progress; return last err
Merge pull request #195 from mreiferson/diskqueue_195

nsqd: deleting topic/channel w/messages on disk orphans files
add max_msg_timeout and msg_timeout to IDENTIFY response
add client configurable output buffering