Added composer.json

For usage see http://getcomposer.org/doc/01-basic-usage.md
Changed composer.json name
Added autoload to composer.json
Moved source to src/ directory and set autoload in composer.json
Moved source to src/ directory and set autoload in composer.json
Changed description in composer.json
Merge pull request #9 from fabiancz/composer

Add Composer metadata, move library to src subfolder