Maintenance release

Improvements:

• supporting HTTPS endpoints for version inference (meta-schema locations) reported and fixed by @rjlohan
• permitting override of built-in format validators - reported and fixed by @luismoramedina
• possible performance improvement by omitting stacktraces of internal exceptions - reported in #318
• dependency updates

Bugfixes:

• fixing JRE implementation-dependent behavior of Validationexception - reported in #319
• properly printing "id" or "$id" depending on draft version when string-serializing Schema instances - reported in #327
• fixing reference lookup by "$id" not working with remote references - reported in #321