UniRx support

[jdnichollsc]

It's possible to integrate UniRx using Conditional compilation symbols.
Actions to execute:

• Move the promises logic to another folder called Promises and add Conditional compilation to detect the dependency.
• Create a new file in order to import UniRx using Conditional compilation too, we can use Overloaded methods or create different names (check the standard here).

[jdnichollsc]

Conditional compilation to detect the dependency is not posible :/