Features:
- Allow search term boosting in relevance score calculation, e.g. `faceted^2
search browsing^0.5`.
Security fixes:
- Update minimum Werkzeug version to 0.15.3. See
[CVE-2019-14806](https://nvd.nist.gov/vuln/detail/CVE-2019-14806): "Pallets
Werkzeug before 0.15.3, when used with Docker, has insufficient debugger PIN
randomness because Docker containers share the same machine id."
Other changes:
- Update jQuery version to 3.4.1.
- Update French translations (translate boolean search operators).
- Improve search form validation and error display.
- Disable not-so-intuitive boolean search operators (`AndNot`, `AndMaybe`,
`Require` were unwanted but enabled by default by Whoosh's `OperatorsPlugin`).
- Improve documentation.
- Code cleanup.