Add Primus to Real-time

[Primus](https://github.com/primus/primus) - An abstraction layer for real-time frameworks to prevent module lock-in.

> ### Advantages
> 
> 1. Effortless switching between real-time frameworks by changing one single line
>   of code. No more API rewrites needed when your project requirements change,
>   the framework gets abandoned or simply breaks down.
> 2. Built-in reconnect, it just works. The reconnect is controlled by a
>   randomised exponential back-off algorithm to reduce server stress.
> 3. Offline detection, Primus is smart enough to detect when users drop their
>   internet connection (switching WIFI points/cell towers for example) and
>   reconnects when they are back online.
> 4. Automatically encodes and decodes messages using custom parsers. Can be
>   easily switched for binary encoding for example.
> 5. A clean, stream-compatible interface for the client and server. You can
>   just `stream#pipe` data around. In addition to that, the client works on
>   Node.js as well, write once, run it everywhere.
> 6. Fixes various of bugs in the supported frameworks and additional stability
>   patches to improve real-time communication.
> 7. Comes with an amazing plugin interface to keep the core library as fast and
>   lean as possible while still allowing the server and the client to be
>   extended.