Maintenance release

NOTE: If you are experiencing lousy producer performance, try setting the linger.ms configuration property to 100 (ms).

Noteworthy critical bug fixes

• Fix OpenSSL instability on Windows (fix thread id callback) - the bug resulted in SSL connections being torn down for no apparent reason.
• Fetch response fix: read all MessageSets, not just the first one. (#1384) - Huge performance degradation (compared to v0.9.5) when fetching small batches.

Enhancements

• Add api.version.request.timeout.ms (#1277, thanks to @vinipuh5)
• Point users to documentation when attempting to use Java security properties (#1412)

Fixes

• Adjust log level for partial message reads when debug is enabled (#1433)
• Allow app metadata() requests regardless of outstanding metadata requests (#1430)
• Proper size calculation from flags2str to include nul (#1334)
• Thread-safe rd_strerror() (#1410)
• Proper re-sends of ProduceRequests in-transit on connection down (#1390)
• Producer: invalid offsets reported back when produce.offset.report=false
• Consumer: Message Null Key/Value were messed up (regression in v0.11.0, #1386)
• Fix metadata querying for topics with LEADER_UNAVAIL set (#1313)
• Treat request __TIMED_OUT as a retryable error
• Let timed out ProduceRequests result in MSG_TIMED_OUT error code for messages
• Fix crash on leader rejoin when outstanding assignor metadata (#1371)
• sasl_cyrus: Fix dangling stack ptr to sasl_callback_t (#1329, thanks to @gnpdt )