expression: Add regexp support

[ajnavarro]

No description provided.

[codecov-io]

Codecov Report

Merging #105 into master will increase coverage by 0.34%.

@@            Coverage Diff            @@
##           master    #105      +/-   ##
=========================================
+ Coverage   60.56%   60.9%   +0.34%     
=========================================
  Files          40      40              
  Lines        1709    1673      -36     
=========================================
- Hits         1035    1019      -16     
+ Misses        615     594      -21     
- Partials       59      60       +1

Impacted Files	Coverage Δ
sql/parse/parse.go	56.22% <ø> (-0.53%)	❌
sql/expression/comparison.go	39.74% <52.38%> (+5.84%)	✅
mem/table.go	57.57% <ø> (-3.54%)	❌
git/objects.go	75% <ø> (-2.15%)	❌
git/blobs.go	75% <ø> (-2.15%)	❌
git/tags.go	80.95% <ø> (-1.27%)	❌
git/references.go	80.95% <ø> (-1.27%)	❌
sql/plan/sort.go	67.94% <ø> (-1.19%)	❌
git/commits.go	81.81% <ø> (-1.17%)	❌
git/tree_entries.go	82.22% <ø> (-1.12%)	❌
... and 9 more

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