Function for parsing all dicom files in a folder

[notZaki]

This PR adds the function dcmdir_parse which reads all DICOM files in a given folder and returns them as an array.

[codecov]

Codecov Report

Merging #57 into master will increase coverage by 0.30%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #57      +/-   ##
==========================================
+ Coverage   87.82%   88.12%   +0.30%     
==========================================
  Files           1        1              
  Lines         312      320       +8     
==========================================
+ Hits          274      282       +8     
  Misses         38       38              

Impacted Files	Coverage Δ
src/DICOM.jl	88.12% <100.00%> (+0.30%)	⬆️

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