Save compatible version of filenames, arrays and ccds function

[siddharthlal25]

This PR will mostly be taken from #30 with some minor modifications.

[codecov]

Codecov Report

Merging #33 into master will increase coverage by 3.20%.
The diff coverage is 88.70%.

@@            Coverage Diff             @@
##           master      #33      +/-   ##
==========================================
+ Coverage   88.14%   91.35%   +3.20%     
==========================================
  Files           5        5              
  Lines         135      185      +50     
==========================================
+ Hits          119      169      +50     
  Misses         16       16              

Impacted Files	Coverage Δ
src/CCDReduction.jl	100.00% <ø> (ø)
src/collection.jl	87.20% <88.33%> (+17.76%)	⬆️
src/fits.jl	100.00% <100.00%> (ø)

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[siddharthlal25]

I will rename df to collection at the end of the PR to keep the diff clean for reviewing.

[siddharthlal25]

@mileslucas @giordano this one is ready for review! Let me know your thoughts about the code.

[siddharthlal25]

I have made a small change, I have exported the functions data and hdr to be accessible by the user for convenience and uniform interface. Thoughts?

[siddharthlal25]

I am merging this one! Thanks for the help and reviews!