Maintenance Release

• References librdkafka version 0.11.5, inheriting associated bug fixes. For more information refer to https://github.com/edenhill/librdkafka/releases/tag/v0.11.5
• The Avro generic serializer now works with multiple topics (thanks @NikolayDekov).
• Fixed a GC cleanup ordering issue during client finalization.
• CentOS 7 compatibility out of the box.

Note: we are no longer adding features to the 0.11.x branches of the .NET Client (but will continue to do maintenance releases for the foreseeable future). All new feature work is being directed towards the upcoming 1.0 release, which contains breaking API changes.