Consider panicing (or similar) for functions without return values

[stapelberg]

Split out of #1

From @fatih:

func foo() {
	// I want to panic here
	bar()

}

func bar() error {
	return errors.New("foo")
}

When I call :GoExpandErr when my cursor is on bar()~ inside foo()` I got this error:

2017/12/28 18:04:49 current function returns no values, cannot return error

I think if there are no returns, it should default to panic(err.Error()) or something alike.

[stapelberg]

It’s not entirely clear to me whether we should panic, log.Fatal (which is what I prefer to use), or even make this configurable. Thoughts?

[fatih]

It’s not entirely clear to me whether we should panic, log.Fatal (which is what I prefer to use), or even make this configurable. Thoughts?

Could this be a setting maybe that user can define? I'm not sure how feasible it would be, but worth trying it out.

[stapelberg]

I think we could allow users to specify a Go template expression.

This should be a reasonably easy task for newcomers to contribute to the project. Applied the help wanted label.