Make Fn Developer Experience awesome on windows

[zootalures]

This is a tracking ticket to cover all the things we should do to make Fn work "nice" for windows developers.

Goal: If you have docker4windows set up, it's as easy to run fn on windows as it is on a mac.

Current state of affairs:

Fn start broken:

fn.exe start 

docker: Error response from daemon: Mount denied:
The source path "C:/Users/Owen Cliffe/.fn/iofs"
doesn't exist and is not known to Docker.
See 'docker run --help'.
2019/03/31 15:21:33 Error: processed finished with error exit status 125

• Invalid Mode: /tmp/iofs : https://github.com/fnproject/fn/issues/1447
• Mount denied: https://github.com/fnproject/fn/issues/1446
• fn start gives two mount warnings in Windows 10 https://github.com/fnproject/fn/issues/1268
• Fn cli is not signed, have to run in developer mode : https://github.com/fnproject/cli/issues/560
• Fn cli colors don't work on windows: https://github.com/fnproject/cli/issues/561

[Daniel15]

Docker on WSL2 might make Windows fixes unnecessary, as the experience should be closer to Docker on Linux: https://engineering.docker.com/2019/06/docker-hearts-wsl-2/