code: func WrapSkipping(e error, skip int) Error {
  	switch e1 := e.(type) {
  	case nil:
  		return nil
  	case *merryErr:
  		return e1
  	default:
  		return &merryErr{
  			err:   e,
  			key:   stack,
  			value: captureStack(skip + 1),
  		}
  	}
  }
docs: // WrapSkipping turns the error arg into a merry.Error if the arg is not
  // already a merry.Error.
  // If e is nil, return nil.
  // If a merry.Error is created by this call, the stack captured will skip
  // `skip` frames (0 is the call site of `WrapSkipping()`)