[ml] Makes StandardScalers state package private and reduce redundant code. Adjusts flink-ml readme.

[FLINK-1844] [ml] Add MinMaxScaler implementation in the proprocessing package, test for the for the corresponding functionality and documentation.

This closes #798.

This closes #796.

Closes #806

The switch was already there: enableObjectReuse() in ExecutionConfig.
This was simply not considered by the streaming runtime. This change now
draws a copy before forwarding an element to a chained operator when
object reuse is disabled.

- remove Maven dependencies
- add docs to show how to register your own serializer with Kryo

This closes #794.

Closes #787

Closes #778

This is a temporal workaround for a bug in hbase.

Closes #800

* register decompression algorithms with file extensions for extensibility
* fit deflate decompression into this scheme
* add support for GZIP files
* test support for deflate and GZIP files with the CsvInputFormat
* replace Apache Commons' Validate with Guava's Preconditions
* add documentation on reading compressed files

This closes #762.

This closes #729.

This closes #788

This closes #774

This closes #784

[flink-core] Added the member currentSplit to FileInputFormat. This member contains the split that this parallel instance must consume.

This closes #791

This closes #795

Closes #771

Closes #789

This closes #781

This closes #786

The fix was done by gyfora in fdac963d.

This closes #793

The context can be used to emit elements and retrieve the checkpointing
lock object.

In the future, the context can be extended to provide support for
element emission with timestamps and dealing with the watermark system.

[tests] Increase timeouts for process failure tests in order to compensate for volatile CI environments (Travis)

This closes #783

 - WebClient assembler class flag is '-c' (not 'assembler')
 - doc-building script is named 'build_docs.sh' (not '_build_docs.sh')