Bump version to v0.11.6

Version v0.11.6-RC1

appveyor: Fix Win32OpenSSL 1.0.2p download link

NuGet: change runtime from win7-.. to more generic win-.. (CLIENTS-1188)

confluentinc/confluent-kafka-dotnet#513

NuGet: change runtime from win7-.. to more generic win-.. (CLIENTS-1188)

confluentinc/confluent-kafka-dotnet#513

Remove incremental from AdminOptions

There is still no concensus in AK how to do incremental configuration
updates so instead of us providing a no-op interface now that might
not match the future Java API, we back out the public portions
but keep the internal implementation for later re-use.

Remove incremental from AdminOptions

There is still no concensus in AK how to do incremental configuration
updates so instead of us providing a no-op interface now that might
not match the future Java API, we back out the public portions
but keep the internal implementation for later re-use.

Fix win32 compilation errors and warnings

rdkafka_performance: simulate consumer processing time with -r <rate>

test 0081: AK v2.0.0 fixes error code DescribeConfigs on unknown topic

This also makes sure topics are created explicitly and not relying
on auto topic creation, for that same test.