ENH: Better support for itk/sitk plugins (#530)
ENH: Better support for itk/sitk plugins (#530)

* ENH: Add nifti suffixes to ITK_FORMATS

* ENH: Add support for itk/sitk reader arguments

pixel_type is relevant for both itk and sitk
fallback_only is True/False - itk only

* ENH: Do not pass args if both are None
imageio/imageio