Add skip_run so build only works on windows

[joeyak]

Since there is no /usr/bin/true for windows or an executable close to it I added a flag to skip the run step. I originally followed #365 by creating an empty go program, but then realized I would have to add true.exe to my repo.

[zoop-btc]

I'm in need of this too since I use nixos but other devs don't the path to "true" won't be the same.

[joeyak]

@praxxus11 I've fixed the merge conflicts

[xiantang]

[build]
  cmd = "go build -o ./tmp/main ."
  bin = "echo"  # Will work on both Windows and Unix-based systems

can u try this?

[joeyak]

It doesn't look clean, but it does work in the end