Update the code to v0.16

[mickeyvip]

Hello,

Can you please update the README.md to v0.16?

port count = length <~ stamps

There is no (<~) and (~) operators as far as I understand. I am not an expert, but think it should be something like:

port count = Signal.map length stamps

Thank you.

[clembu]

with 0.18 now you don't ever have implementation of ports, from what I gather. Also there are Cmd and Sub types in Platform module of Core package