aw-query: Add preprocessing and refcounting

[johan-bjareholt]

A very unsophisticated way to refcount.

TODO:

• Lots of TODOs in code
• Value is cloned even if variable is overwritten
• Run more benchmarks

[codecov]

Codecov Report

Merging #183 into master will decrease coverage by 8.70%.
The diff coverage is 19.35%.

@@ Coverage Diff @@ ## master #183 +/- ## ========================================== - Coverage 59.07% 50.36% -8.71%  ========================================== Files 58 60 +2 Lines 7707 8146 +439 Branches 2311 1537 -774 ========================================== - Hits 4553 4103 -450  - Misses 3104 4031 +927  + Partials 50 12 -38 

Impacted Files	Coverage Δ
aw-query/src/preprocess.rs	0.00% <0.00%> (ø)
aw-query/src/varenv.rs	0.00% <0.00%> (ø)
aw-query/src/lib.rs	27.50% <20.00%> (-20.33%)	⬇️
aw-query/src/interpret.rs	59.90% <42.85%> (-20.62%)	⬇️
aw-query/tests/query.rs	69.58% <55.55%> (-22.06%)	⬇️
aw-query/src/functions.rs	91.69% <100.00%> (-0.29%)	⬇️
aw-query/src/lexer.rs	33.89% <0.00%> (-57.07%)	⬇️
aw-query/src/parser.rs	27.45% <0.00%> (-18.78%)	⬇️
... and 6 more

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