Providing a more fluent api to ngStomp Service

[davinkevin]

We have now some parameters for each functions, so it's simple to mix up the order of parameters. For example :

ngstomp
        .subscribe('/topic/item', whatToDoWhenMessageComming, {}, $scope)

We have 4 parameters :

• topic pseudo url
• 'callback' for each data received
• header object to send when subscribe
• the $scope for later un-subscription

Some parameters are optional, like the scope and the headers, so if you want to unsubscribe from scope, you have to send useless object describing the headers...

I want to add a more intuitive and fluent API like this (proposition) :

ngstomp
        .subscribeTo('/topic/item')
                .callback(whatToDoWhenMessageComming)
                .withHeaders({})
                .bindTo($scope)
        .build() /* ... or something else */

And if we have multiple subscribe :

ngstomp
        .subscribeTo('/topic/item')
                .callback(whatToDoWhenMessageComming)
                .bindTo($scope)
        .and()
        .subscribeTo('/topic/item')
                .callback(whatToDoWhenMessageComming)
                .withHeaders({})
        .build();

Let me know if you have a better idea and help with PR ;)