Add back client library links removed for an unknown reason
Add back client library links removed for an unknown reason

I could not add back the .NET reference links since I couldn't find
references for latest stable, 5.0.1. This is a list of all .NET client
references that we publish: https://www.rabbitmq.com/releases/rabbitmq-dotnet-client/
Notice that the last published version is v3.6.14

Same as above for the Erlang client: https://www.rabbitmq.com/releases/rabbitmq-erlang-client/

We are publishing Javadoc: https://www.rabbitmq.com/releases/rabbitmq-java-client/current-javadoc/

fixes #474

cc @lukebakken @kjnilsson @dumbbell @michaelklishin

rabbitmq/rabbitmq-website,rabbitmq/rabbitmq-website,rabbitmq/rabbitmq-website,rabbitmq/rabbitmq-website,rabbitmq/rabbitmq-website