[FLINK-1086] Replace JCL with SLF4J and Log4j with LOGBack

- Excluded Kafka's transitive dependencies: jmxtools and jmxri
- Corrected encoder pattern in logback.xml
- Removed explicit logging access. Loggers are now configured by
  configuration files. Fixed Yarn issue with multiple logging
  bindings.

This closes #111.
[FLINK-1017] Add documentation for execution parallelism

This closes #114
Updated documentation figure: FlinkOnYarn.svg

This closes #110
[FLINK-629] getFieldNotNull added to Tuple and updated Aggregators and Comparators to use that where appropriate
[FLINK-629] Updated getFieldNotNull usage and added it to TupleSerializers

This closes #73
[FLINK-1063] Revert race introducing commit

This reverts "[FLINK-998] Close network connections when idle" [1] as
it introduced a race condition into the network stack, which might
result in a re-ordering of network envelopes.

[1] 52512636444902497e47ccbfb1cabaffb3e23343
[FLINK-925] Support KeySelector function returning Tuple types
[FLINK-925] Extended for distinct operator and added test cases

This closes #59
Fix typo in package LICENSE
Remove space after comma for TupleXX.toString()