Code enhancements and test data for file mode geoid interpolation

[rogerfraser]

This pull request provides some minor enhancements to geoid and includes two sample test datasets and test coverage scripts for file mode geoid interpolation (via the --text-file arg option)

[codecov-io]

Codecov Report

Merging #89 (322e75e) into master (e4f85c7) will increase coverage by 0.66%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master      #89      +/-   ##
==========================================
+ Coverage   59.84%   60.50%   +0.66%     
==========================================
  Files         117      117              
  Lines       33946    33948       +2     
==========================================
+ Hits        20314    20541     +227     
+ Misses      13632    13407     -225     

Impacted Files	Coverage Δ
...just/dynadjust/dnageoidwrapper/dnageoidwrapper.cpp	64.30% <66.66%> (+4.61%)	⬆️
...t/dynadjust/dnaadjustwrapper/dnaadjustprogress.cpp	50.82% <0.00%> (-1.11%)	⬇️
dynadjust/include/functions/dnastrmanipfuncs.hpp	71.42% <0.00%> (+1.68%)	⬆️
dynadjust/include/functions/dnastringfuncs.cpp	96.15% <0.00%> (+3.84%)	⬆️
dynadjust/dynadjust/dnageoid/dnageoid.cpp	43.57% <0.00%> (+14.00%)	⬆️
dynadjust/include/exception/dnaexception.hpp	33.33% <0.00%> (+14.81%)	⬆️

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