Fixed recursive locking on broker fail+buf retry (issue #27)
Changed stats counters to atomics
Added socket.send.buffer.bytes and socket.receive.buffer.bytes configuration properties
Added rd_kafka_version() and rd_kafka_version_str()

This is needed for runtime acquisition of the version when linking dynamically.
Updatd configuration link
Fixed typo in INTRODUCTION
Correctly calculate number of topics for filtered Metadata requests

Reported by Steven Le Roux
Removed debug-assert from last commit.
Only generate statistics if statistics.interval.ms is non-zero

Reported by Eugenio Peréz Martín
Merge branch 'master' of github.com:edenhill/librdkafka