Allow plugin to accept array of payload objects.

[joshferrell]

Description

Allow plugin to send array of address. Route could look something like this

server.route({
    method: 'POST',
    path: '/',
    handler: {
        email: {
            subject: 'test',
            component: SimpleEmail
        }
    },
    config: {
        validate: {
             payload: joi.array().items(joi.object({
                   email: joi.string().required()
             }
       }
    }
});