Add composer support

[Ali1]

Thanks for the useful plugin

[Ali1]

?

[Ali1]

Go here https://github.com/segy/PhpExcel/new/master
Call it composer.json

{
    "name": "segy/PhpExcel",
    "description" : "PhpExcel helper and component for CakePHP 2.x",
    "license" : "WTFPL",
    "type" : "cakephp-plugin",
    "authors": [],
    "require" : {
        "composer/installers": "*"
    }
}