Can not create an empty FITS file

[jishnub]

Currently it is not possible to create an empty fits file, one with minimal header information, something along the lines of what's presented here: esheldon/fitsio#164 (comment). This would be a nice feature to have.

[jbrinchmann]

I was looking at this because I need it too. Maybe I'm wrong about this but it seems to me that this is a limitation not of FITSIO (alone) but rather of CFITSIO because the fits_create_img function does not allow for Null data (which is how python's fitsio is dealing with this).

[jbrinchmann]

I left an issue at JuliaAstro/CFITSIO.jl#19 where I also include code to create an empty HDU using CFITSIO.