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.
[streaming] Fixed SlidingWindowStateIterator
[streaming] Reduce operator added to ConnectedDataStream + test
[streaming] Updated directed emit to not use output names when all outputs are selected
[FLINK-1080] [streaming] Streaming aggregation added

Conflicts:
	flink-addons/flink-streaming/flink-streaming-core/src/main/java/org/apache/flink/streaming/api/datastream/DataStream.java
[streaming] Added TypeInfo to DataStream
[FLINK-1080] [streaming] Streaming aggregation update and refactor
[FLINK-1058] [streaming] Streaming initial documentation
[streaming] DataStream type refactor for easier future extensions
[streaming] Invokables and tests added for fast batch/window reduce operations and aggregations
[streaming] window and batch operator added to DataStream + Documentation updated accordingly
[streaming] Updated logging to utilize SLF4J
[streaming] Added CoBatchGroupReduceInvokable, CoWindowGroupReduceInvokable and grouped variants
[streaming] Added counter aggregation
[streaming] Added checked exception to execution
[streaming] GroupedBatchReduce modified to batch by key, updated WindowReduce + Batch/Window reduce refactor
[streaming] Minor bug fixes in Connectors, StreamCollector & docs

This closes #115
[FLINK-989] Improve error message when not finding enough task slots.
[FLINK-1030] Refactor and clean up instance managers.
[FLINK-1094] Reworked, improved, and testes split assigners