Const casting to make g++ happy (issue #36)
Handle per topic+partition produce errors (issue #40)

Produce errors were previously only handled if the entire request failed.
Fixed output typo in rdkafka_performance
Added -I (idle) switch to rdkafka_performance

The Idle switch turns off producing any messages.
Updated README on Debian packages and C++
Fixed typo in example programs (issue #44)
rdkafka_performance: Count immediate produce() failures as failed messages too
Use 'void *' for produce payload type instead of 'char *'

This avoids the need for casting in the application.
Allow NULL 'conf' argument to rd_kafka_topic_new()