This closes #1751.

This closes #1749.

This closes #1743

This closes #1737

This brings it more in line with *ProcessingTimeWindows and makes it
clear what type of window assigner it is.

The old name, i.e. SlidingTimeWindows and TumblingTimeWindows is still
available but deprecated.

This enforces that the user always has to specify keys for both inputs
before .window() can be called.

This closes #1732.

This closes #1735.

The current flink-gelly-examples artifact id wrongly used an underscore to separate
examples from flink-gelly. This commit replaces the underscore with an hyphen.

This closes #1731.

This closes #1716.

This closes #1700.

Closes #1730

This implicitly adds KeyedStream.transform() and also explicitly
ConnectedStreams.transform().

This also removes the transform exclusions from the API completeness
tests.

This makes AllWindowedStream.fold() take constant space, just like the
keyed WindowOperator.

Also this adds a new test case in EventTimeAllWindowCheckpointingITCase
to verify that the FoldingWindowBuffer works.

This also renames the preexisting window buffers to ReducingWindowBuffer
and ListWindowBuffer to make the naming scheme consistent.

This closes #1723

This closes #1727

This closes #1725

The new flink-gelly-examples module contains all Java and Scala Gelly examples. The module
contains compile scope dependencies on flink-java, flink-scala and flink-clients so that
the examples can be conveniently run from within the IDE.

This closes #1719

[FLINK-3522] [storm compat] PrintSampleStream prints a proper message when involked without arguments

This also includes some minor cleanups

This closes #1689

Temporary work around to restore initial state on failure during recovery as
required by a user. Will be superseded by FLINK-3397 with better handling of
checkpoint and savepoint restoring.

A failure during recovery resulted in restarting a job without its savepoint
state. This temporary work around makes sure that if the savepoint coordinator
ever restored a savepoint and there was no checkpoint after the savepoint,
the savepoint state will be restored again.

This closes #1720.

This closes #1714

* Explicitly state to stop the local environment

This closes #1718

This makes sure that for bounded data sets with watermarks, the final elements get properly reflected in window results.

This closes #1675

This closes #1695