IRRd 4.1.0 release candidate 1

https://irrd.readthedocs.io/en/v4.1.0rc1/
This rc1 release has a new database migration, so you have to run irrd_database_upgrade even if you were running beta 4 already.
Unless any issues are found, this is planned to be the 4.1 release.

Changes:

• Convert whois handling to use long-running workers (and reduced max_connections default to 10 to reduce default memory use)
• Add scope filter (#4)
• Add better handling of exports when serials are unknown (#356)
• Add !J command and modified !j command (#339, #322)
• Add last-modified attribute to authoritative objects (#290)
• Add support for custom logging configs (#299)
• Only log NRTM RPKI status for relevant objects when RPKI is enabled
• Add support for database downgrades and docs in 4.1 release notes (#333)
• Consistently log query time in same number of decimals.
• Read RPSL files iteratively, reducing IRRd memory usage. (#342)
• End RIPE-style whois responses with two empty lines. (#335)
• Ignore trailing slash in status page URL (#336)
• Add note about maxmemory Redis setting to docs. (#323)