True\Punycode methods can be use with static access

Because I wanted to do this with your library 
```php
// Import Punycode
use True\Punycode;

// Use UTF-8 as the encoding
mb_internal_encoding('utf-8');

echo Punycode::encode('renangonçalves.com');
// outputs: xn--renangonalves-pgb.com
echo Punycode::encode('xn--renangonalves-pgb.com');
// outputs: renangonçalves.com

echo Punycode::encodeLabel('renangonçalves');
// outputs: xn--renangonalves-pgb
echo Punycode::encodeLabel('xn--renangonalves-pgb');
// outputs: renangonçalves

```
I've made the following cosmetic changes:

* add public static access to the following functions:
    * `encode`
    * `decode`
    * `encodePart` renamed `encodeLabel` as they are referred to in the [RFC 3490](http://tools.ietf.org/html/rfc3490#section-4.1)
    * `decodePart` renamed `decodeLabel` as they are referred to in the [RFC 3490](http://tools.ietf.org/html/rfc3490#section-4.1)

* I've update the project setting to:
    * validate the library on upcoming `PHP 5.6` and `hhvm`
    * add the `composer.lock` file in the `.gitignore`
   * to generate to generate the code coverage results with `phpunit.xml.dist`

**Of Note: This does not in anyway change the current library behaviour**