v2020.075

• Fix resuming SeedLink connections when both sequence and begin time are included in multi-station mode.
• Add IPv6 support, on by default if supported by the system.
• Add ability to serve variable miniSEED record lengths via SeedLink.
• Add ability to scan variable miniSEED record length via file scanning.
• Apply LimitIP SourceID pattern to limit what a client can write in addition to read.
• Update libmseed to 2.19.6.
• Update mini-XML library to 3.1.
• Update pcre library to 8.43.
• License ringserver specific code as Apache 2.