Support formatting from stdin so golines can be used directly with VS Code's Go extension

[jbcpollak]

I would like to use golines in VS Code but I'd like to avoid using an additional extension. If golines could support formatting on stdin and then writing to stdout (it already does that) it could be used as a custom formatter directly in VS Code. See the description below:

I assume this would have utility for other IDEs and toolchains as well.