properly define get() instead of getkey()

[aplavin]

the current getkey() behavior should actually be get(): getkey in julia returns the key, while get returns the value

[codecov[bot]]

Codecov Report

Merging #184 (77e0b4f) into master (b272b28) will increase coverage by 0.02%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #184      +/-   ##
==========================================
+ Coverage   91.26%   91.29%   +0.02%     
==========================================
  Files           5        5              
  Lines         687      689       +2     
==========================================
+ Hits          627      629       +2     
  Misses         60       60              

Impacted Files	Coverage Δ
src/FITSIO.jl	100.00% <ø> (ø)
src/header.jl	86.38% <100.00%> (+0.14%)	:arrow_up:

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[aplavin]

I just wanted to avoid breaking changes: make it a deprecation for now, and then make a breaking release later when some other breaking changes are gathered. I strongly believe that the proper getkey fix has to be a breaking release (minor version), as it's a pretty common function changing behavior.

[mileslucas]

I have no qualms with a breaking release, I say go for it.

[aplavin]

Maybe do both? Add get & deprecate the current getkey in a non-breaking release, and then implement the proper getkey behavior in a breaking one. I've added another commit following your comments. After merging, you can register both versions: from the first and second commits. Both commits passed CI tests here.

[mileslucas]

That sounds like a good idea. Thanks for the help!