[FLINK-610] Added KryoSerializer

This closes #74
Default generic serializer is Avro. Minor improvements in KryoSerializer. Add mini benchmark for Avro/Kryo.
Disable merging of Iteration Aux Tasks

This will become obsolete once we have buffer oriented execution.
Disable it for now because it is causing a bug: FLINK-1087
Fix DeltaIteration Bug with Immutable Types

The CompactingHashTable did not obey the new serialization contract that
allows for immutable objects. We must always use the return value of the
deserialization methods and cannot assume that the data was put into the
reuse object.
[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
[Tools] Minor fixes in release script

- Introduced required RELEASE_BRANCH environment variable
- Some hardcoded binary calls (gpg, sha512sum, md5sum) have been
  replaced by environment variables (GPG, SHASUM, MD5SUM) and added
  "" argument for 'sed -i' calls for compatability with OS X
- Removed unused environment variables
- Directly call ssh/scp instead of going through sshpass
Fix typo in CONTRIBUTORS

Fixes a typo in CONTRIBUTORS, replaces tabs by whitespaces for alignment,
and updates email adresses of Apache committers to @apache.org.
Update CONTRIBUTORS file

Updates CONTRIBUTORS file with contributors from 0.6-incubating release
announcement and sorts by first name.
[FLINK-1097] Fixed multiple slf4j bindings when using Hadoop2

I excluded all slf4j-log4j12 transitive dependencies to get rid off the warning that slf4j finds multiple slf4j bindings in the classpath. Additionally, I added log4j-over-slf4j and excluded all log4j transitive dependencies so that slf4j handles also legacy log4j logging messages from dependencies.

Author: Till Rohrmann <trohrmann@apache.org>

Closes #121 from tillrohrmann/FLINK-1097 and squashes the following commits:

b9f76d5 [Till Rohrmann] Excluded slf4j-log4j12 as transitive dependency in order to not have multiple slf4j bindings in the class path. Added log4j-overslf4j and excluded log4j transitive dependencies to collect log4j outputs.
Remove naive verification of tuple size

This verification will not work.
Think of spaces or escaped ?
I think it's easier for users to parse the SQLException

Author: Moritz Schubotz <github@ckurs.de>

Closes #116 from physikerwelt/patch-1 and squashes the following commits:

69a3d2a [Moritz Schubotz] Remove associated test as well
b51b4f0 [Moritz Schubotz] Remove naive verification of tuple size
Remove space after comma for TupleXX.toString()

It is better to save some bytes when writing the output. Users can always overwrite to `toString()` if they want.

Author: Robert Metzger <rmetzger@apache.org>

Closes #118 from rmetzger/benchFixes and squashes the following commits:

cb8a251 [Robert Metzger] Remove space after comma for TupleXX.toString()
Remove CONTRIBUTORS file to prefer dynamically generate it

Per discussion in the dev@ list, maintaining the CONTRIBUTORS file manually is hard to do.

Most ASF projects defer this to team page or retrieveing it from JIRA or git commit list
for every release if needed.

This PR proposes to remove it and defer to dynamically created per release.

Author: Henry Saputra <henry.saputra@gmail.com>

Closes #123 from hsaputra/remove_contributors_file and squashes the following commits:

e235cbc [Henry Saputra] Per discussion in the dev@ list maintaining the CONTRIBUTORS file manually is hard. Most ASF projects defer this to team page or retrieveing it from JIRA or git commit list for every release.