Release Candidate for 2.0.0

Introduced a BC.

the contructor was:
``` php 
    /**
     * @param \Liuggio\StatsdClient\Sender\SenderInterface $sender
     * @param Boolean $reducePacket
     * @param Boolean $fail_silently
     */
    public function __construct(SenderInterface $sender, $reducePacket = true, $fail_silently = true)
    {
```
and with this PR is:
``` php 
   /**
     * @param SenderInterface $sender
     * @param boolean         $fail_silently
     */
    public function __construct(SenderInterface $sender, $fail_silently = true)
```

The packet reducer is now act as decorator:

see the [README.md](https://github.com/liuggio/statsd-php-client/blob/rc_2_0/Readme.md)