Make this library usable with composer

[Yopai]

Hi,

In order this library can be used with composer, there are three things to do :

• create a composer.json
• move the class into its own namespace, in a directory "src"
• register the package into packagist.org

This PR covers the two first steps.

I saw this is quite an old project; do you want me to do the packagist registration ?