PlusCal specification for Event Driven HotStuff algorithm

[Steve Thornton]

I've created a specification for the Event Driven HotStuff algorithm as described in 

HotStuff: BFT Consensus in the Lens of Blockchain (arXiv: 1803.05069v6 [CS.DC]), Algorithms 4 and 5.

This is my first try at writing a non-trivial spec, so constructive criticism is very welcome.

You can find it here https://github.com/ausimnull/EDHotStuff

I hope this may be of interest to some of the community, as HotStuff is currently gaining a lot of attention.

best regards

Steve (ausimnull)