add composer.json to reuse for PHP develop

Add composer.json to reuse for PHP develop.
and Could you consider register this repository to packagist.org ?

- composer
https://getcomposer.org/doc/00-intro.md
- to submit Packagist
https://packagist.org/packages/submit

If you finished to register into packagist, we can setup simply like as below.
`php composer.phar require woothee/woothee`