### Motivation

A user was attempting to use the existing HDFS connector to connect to a 2.x version of HDFS, but the current connector only supported 3.x version of HDFS. 

### Modifications

To address this issue, we renamed the current HDFS connector to HDFS3, and created a new 2.x compatible connector named HDFS2. 

The code in both of these are nearly identical with 2 notable exceptions. First and foremost, they both use different versions of the Hadoop-client library. And secondly, the HDFS2 version creates the FSDataOutputStream object directly, whereas the HDFS3 version leverages the FSDataOutputStreamBuilder class for this purpose, as it is the preferred method going forward.

### Result

There will be be support for connecting to both 2.x and 3.x version of HDFS. However, there MAY BE some library conflicts in the released jar due to the different versions of the same library in the different modules. Hopefully the NAR packaging will address this.

### Motivation

Added a sink connector that writes JSON documents into ElasticSearch

### Modifications

Added new pulsar-io module and associated integration tests

### Result

An ElasticSearch sink connector will be available for use.

* Added HDFS Sink

* Fixed issues identified during PR review

* Fixed comment

* Added HDFS Container to externalServices

* Ignoring HdfsSink test for now

* Removed HDFS Container to externalServices

* Fixed ASL licensing

* Fixed compile errors

* Added HDFS to SinkType Enum

### Motivation

We need to package Pulsar IO connectors as part of the release. 
We provide a new file `apache-pulsar-io-connectors-$VERSION-bin.tar.gz` that contains [NAR](https://medium.com/hashmapinc/nifi-nar-files-explained-14113f7796fd).

In subsequent PR, I'll add the logic to load and use these archives.

Signed-off-by: NSijie Guo <sijie@apache.org>

Remove pulsar-common dependency from pulsar-io-core module and cleanup pulsar-common dependency references (#2020)

*Motivation*

With pulsar-common shading in pulsar-client, conflicts observed when using pulsar-client with connectors. Because pulsar-client shades its dependencies,
while pulsar-io implementations pull in pulsar-common which depends on non-shaded dependencies.

*Changes*

- Move KeyValue class to pulsar-io-core, since all pulsar-io is using it.
- Remove pulsar-common from all pulsar-io implementation modules
- Cleanup all direct usage of pulsar-common when pulsar-client-original is in the place.

* begin renaming process

* more class and directory renames

* move Record classes into pulsar-io

* apply rename to Maven configs

* rename java imports

* update versions in maven configs

* add missing imports

* remove Message class from pulsar-io

* add missing import

* add Reflections util import

* add Utils import

* add missing Record import

* supply missing Record imports

* Added Cassandra Sink Connector

* Added Pulsar Connect interfaces that define connectors that push data into pulsar and take data from pulsar

* Added Twitter connector

* Added hbc core version mapping

* Addressed comments

* Fixed build

* Fixed license header

- Remove function-composition

* Relocate instance and spawner to be under `runtime` package
* fix the pom files and travis build

* Split functions module into api/runtime/api-examples

* Move `org.apache.pulsar.functions.api` package from runtime to api package

* Updates headers with ASF source files header

* change license to additional files