*Motivation*

Bump the development version to 2.6.0-SNAPSHOT

* Add a source connector for MongoDB

* Fix expected license header

### Motivation

Provides a builtin MongoDB Connector, in order to ease the storage of JSON formated message in MongoDB. It's a sink connector.


### Modifications

Add a new sub-module in the `pulsar-io`module.

### Verifying this change

This change added tests and can be verified as follows:
* deploy the connector with configuration file containing the following fields:
```
configs:
  mongoUri: mongodb://hostname:port
  database: pulsar
  collection: messages
```
* start a mongodb instance
* send messages in the topic declared when deploying the connector
* check in MongoDB if the messages have been stored in the collection `messages`

### 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>

* 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 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