Ranked OR TAAT

[amallia]

Since #14 was getting more complicated, I thought it was better to first merge this.

We will squash everything before merging, but basically it includes:

• ranked OR taat
• simple accumulator
• general refactoring of query algorithms

MaxScore and other accumulators will be addressed separately.

[codecov]

Codecov Report

Merging #73 into master will increase coverage by 0.05%.
The diff coverage is 98.88%.

@@            Coverage Diff             @@
##           master      #73      +/-   ##
==========================================
+ Coverage   92.57%   92.62%   +0.05%     
==========================================
  Files          85       87       +2     
  Lines        4914     4961      +47     
==========================================
+ Hits         4549     4595      +46     
- Misses        365      366       +1

Impacted Files	Coverage Δ
include/pisa/freq_index.hpp	100% <ø> (ø)	⬆️
include/pisa/block_posting_list.hpp	98.54% <ø> (ø)	⬆️
include/pisa/query/algorithm/ranked_or_query.hpp	97.29% <100%> (+0.07%)	⬆️
include/pisa/query/algorithm/wand_query.hpp	98.41% <100%> (+0.02%)	⬆️
...lude/pisa/query/algorithm/block_max_wand_query.hpp	99.03% <100%> (ø)	⬆️
include/pisa/query/algorithm/maxscore_query.hpp	98.38% <100%> (ø)	⬆️
.../pisa/query/algorithm/block_max_maxscore_query.hpp	98.68% <100%> (+0.01%)	⬆️
test/test_ranked_queries.cpp	100% <100%> (ø)	⬆️
include/pisa/accumulator/simple_accumulator.hpp	100% <100%> (ø)
test/test_bmw_queries.cpp	100% <100%> (ø)	⬆️
... and 4 more

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