Image from only taking PNG

[myagmartseren]

No description provided.

[oneplus1000]

Thanks for the PR, but I think changing function parameters like this will cause compile errors in old code that uses gopdf. Maybe instead of fixing the old function, you add a new function, something like this.

func (gp *GoPdf) ImageFromWithOption(img image.Image, x float64, y float64, rect *Rect, option OptionForImageFrom) error  {
 ...
}

type OptionForImageFrom struct{
	Format string  // png,jpeg ...
	//... for future additions.
}

[myagmartseren]

Oh good idea