[FEATURE] Add compression to raptor_index

[eseiler]

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[codecov]

Codecov Report

Merging #58 (5e7bc55) into master (caa02cb) will increase coverage by 1.28%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##           master      #58      +/-   ##
==========================================
+ Coverage   84.44%   85.72%   +1.28%     
==========================================
  Files          30       30              
  Lines         977      988      +11     
==========================================
+ Hits          825      847      +22     
+ Misses        152      141      -11     

Impacted Files	Coverage Δ
include/raptor/index.hpp	95.52% <85.71%> (+14.82%)	⬆️
include/raptor/build/store_index.hpp	100.00% <100.00%> (ø)
src/argument_parsing/search.cpp	100.00% <100.00%> (ø)
include/raptor/build/index_factory.hpp	100.00% <0.00%> (+4.00%)	⬆️
src/raptor_build.cpp	57.14% <0.00%> (+7.14%)	⬆️
src/raptor_search.cpp	84.61% <0.00%> (+7.69%)	⬆️

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