Insert a new primary HDU

[jishnub]

Uses PREPEND_PRIMARY as discussed in #16 . Currently I've hard-coded the value here, which is not ideal. This allows one to insert a new primary HDU and convert the pre-existing one to an image HDU.

julia> f = fits_create_file(tempname());

julia> a = ones(3);

julia> fits_create_img(f, a); fits_write_pix(f, a);

julia> fits_get_img_size(f)
1-element Vector{Int64}:
 3

julia> fits_insert_img(f, Float64, [3,2], true); # insert new primary image

julia> fits_get_hdu_num(f) # check that the current HDU index is still 1
1

julia> fits_get_img_size(f) # the original HDU has been replaced
2-element Vector{Int64}:
 3
 2

julia> fits_movabs_hdu(f, 2) # the original primary HDU is now an image
:image_hdu

julia> fits_get_img_size(f)
1-element Vector{Int64}:
 3

[codecov]

Codecov Report

Merging #18 (fd66522) into master (5c376e4) will decrease coverage by 0.18%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #18      +/-   ##
==========================================
- Coverage   77.04%   76.85%   -0.19%     
==========================================
  Files           1        1              
  Lines         588      592       +4     
==========================================
+ Hits          453      455       +2     
- Misses        135      137       +2     

Impacted Files	Coverage Δ
src/CFITSIO.jl	76.85% <100.00%> (-0.19%)	⬇️

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[giordano]

I only wonder if prependprimary should be a keyword argument, but I don't have a strong opinion about that, I'm fine with the current implementation