Improved the composer metadata

[stof]

The keywords and the description will improve its referencing on Packagist and the autoload section allows to use the package without bothering about the location of the file.

Another important missing key in your composer.json is the license one. But I was not able to add it as I haven't found any licensing information in your repository. Could you add it ?

[iamcal]

Thanks for the patch - i'll add a license field now

[stof]

thanks