Interservice communication

[jirenius]

Issue

The service package should support making call requests and getting resources and events from other RES services connected to NATS.

// Example of what the API might be like

// Connect client to NATS
client := res.NewClient("nats://127.0.0.1")

// Sets token used in call requests
client.SetToken(nil)

 // Get resource from another 
books, err := client.Get("library.books")

// Get resource type; res.TypeModel, res.TypeCollection
typ := books.Type()

// Returns a map[string]Value. Panics if books.Type() is not res.TypeModel
m := books.Model()

// Returns a []Value. Panics if books.Type() is not res.TypeCollection
c := books.Collection()

// Unmarshals the resource into the provided interface value
var b []Book
err := books.Unmarshal(&b)

// Subscribe to events
sub := book.Subscribe(func(r res.Resource, ev res.Event) {
    // Handle event
})

// Unsubscribe to events
sub.Unsubscribe()