Show Nim: Mummy, a new HTTP + WebSocket server that returns to the ancient ways of threads

[alexeypetrushin]

This is the step in the right direction (I think it's called the [Reactor 
Pattern](https://en.wikipedia.org/wiki/Reactor_pattern)). It covers most of 
cases needed from the server.

Good job! @boia01 and other implementations are good job too :).