v0.2.0

API Improvements:

• Renames GetState() to GetFullState().
• Introduces a new GetState() that returns only the state value (without the error state), eliminating the need for the if s, _ := x.GetState(); s == nested.Ready { pattern.
• Adds a label parameter to Collection.Add(), so that services in the collection can be referenced.
• Adds the method Collection.Up() to return a map indicating the readiness of all currently monitored services.