Improve struct code-generation for pointer fields

[jmattheis]

For this converter interface

// goverter:converter
type Converter interface {
	Convert(*Input) *Output
}

type Input struct {
	Age  int
	Name *string
}
type Output struct {
	Age  int
	Name *string
}

goverter will generate this code

func (c *ConverterImpl) Convert(source *example.Input) *example.Output {
	var pExampleOutput *example.Output
	if source != nil {
		var exampleOutput example.Output
		exampleOutput.Age = (*source).Age
		var pString *string
		if (*source).Name != nil {
			xstring := *(*source).Name
			pString = &xstring
		}
		exampleOutput.Name = pString
		pExampleOutput = &exampleOutput
	}
	return pExampleOutput
}

This could be simplified to:

func (c *ConverterImpl) Convert(source *example.Input) *example.Output {
	var pExampleOutput *example.Output
	if source != nil {
		var exampleOutput example.Output
		exampleOutput.Age = (*source).Age
		if (*source).Name != nil {
			xstring := *(*source).Name
			exampleOutput.Name = &xstring
		}
		pExampleOutput = &exampleOutput
	}
	return pExampleOutput
}

This is useful for the default feature. See #96 (comment) & #93

Please 👍 this issue if you like this functionality. If you have a specific use-case in mind, feel free to comment it.

[gtchiflidjanov]

This could be simplified more:

func (c *ConverterImpl) Convert(source *example.Input) *example.Output {
  var pExampleOutput *example.Output
  if source != nil {
    pExampleOutput = & example.Output{
      Age: source.Age,
      Name: source.Name,
    }
  }
  return pExampleOutput
}