A rough roadmap for 6.0.0. All input is welcomed.

• Drop java-8 compatibility. First java-11 release [optional, depends on timing and community needs]
• Drop dependency on legacy RCSB PDB services, e.g. source.rcsb.org. Remove code that uses the dependencies.
• Remove BioJava's own mmCIF parser, making the ciftools-java parser the default one (code already in since 5.3.0). Drop all unneeded code.
• Full support for branched entities in structure module (related to PDB carbohydrate remediation appearing in July 2020)
• More clean up of error handling. Throw early, catch late.
• More clean up of tests: reduce external resources need at test time

Process improvements

• Use SonarQube to measure coverage and quality. Hook it up in CI for pull requests (see Add reporting for code coverage  #561 )