fix: #24 operators `in` and `not in` not working correctly with nulli…

…sh types

fix: #24 function `uniq` not working correctly with nullish types

fix: explicitly export TypeScript types

chore: rename a variable for consistency

fix: document function `substring` and change it into a standalone fu…

…nction

Merge branch 'develop'

feat: implement function `if`

chore: update devDependencies

chore: trigger a release

fix: export type definitions like `JSONQuery` and `JSONQueryOptions`