Allow to set a Prefix for the setter functions

[carloscasalar]

I think it would be great to be able to set a prefix for the setter functions.

For example:

//go:generate gonstructor --type=Structure --constructorTypes=builder --setterPrefix=With
type Structure struct {
	foo string
}

Could generate:

type StructureBuilder struct {
	foo        string
}

func NewStructureBuilder() *StructureBuilder {
	return &StructureBuilder{}
}

func (b *StructureBuilder) WithFoo(foo string) *StructureBuilder {
	b.foo = foo
	return b
}

func (b *StructureBuilder) Build() *Structure {
	return &Structure{
		foo:        b.foo,
	}
}