[Ruby] Release 0.50.0

• CanonicalSchema#union and CanonicalSchema#subtract.
• JSONSchema::Canonical::UnsupportedResult, raised where the canonical form does not support a set operation's result.
• JSONSchema::Canonical::IncompatibleOperands where both operands read # and it names a different document on each side.
• JSONSchema::Canonical::Containment, Satisfiability, Distinctness and Kind: named constants for the symbols covers, satisfiability, kind and ArrayView#distinctness return, each with an ALL list.

Changed

• CanonicalSchema#satisfiable? is now CanonicalSchema#satisfiability, answering :yes, :no, or :unknown - :yes wherever a value can be exhibited, not only for the forms listing their members.
• CanonicalSchema#covers decides through the difference as well: :no where the argument keeps values the receiver rejects, :yes where nothing is left over.
• CanonicalSchema#is_subset_of is now CanonicalSchema#covers, answering :yes, :no, or :unknown for whether the receiver admits every value the argument admits.
• CanonicalSchema#negate raises where it used to return nil.
• JSONSchema::Canonical::UnmodeledOperand is now JSONSchema::Canonical::UnsupportedOperand, and means only that an operand is a Raw pass-through.

Fixed

• Combining nodes of two different documents repointing a $ref to # at the combined result instead of the document it was written in, including one named by a definition the result keeps.
• Intersecting a $ref whose target is true or false, which crashed the interpreter.
• A key constraint left un-narrowed once a run is out of intersections, which crashed the interpreter on the next read of it.
• CanonicalSchema#covers answering :unknown for a schema against itself, where that schema is a $ref.
• CanonicalSchema#union keeping a $ref beside the schema it names, where the other three operations read through it.
• CanonicalSchema#covers and CanonicalSchema#subtract cancelling two nodes written the same way whose # names a different document.
• Two results accepting the same values comparing unequal over the part of their documents neither reads.
• additionalProperties reaching a key the pattern map matches when a finite key constraint closes the map, which dropped values both operands accept.
• A recursive definition stopping every other pointer in the document from being read through.
• One $defs entry read past a wider schema written out at every use, rather than kept as the pointer it was.
• Set operations rejecting one document canonicalized twice, and a pruned result rejected against the document it came from, where the maps resolve every shared reference the same way.
• Set operations comparing a $ref as a pointer instead of reading through it, so a schema written with a $ref did not cancel against the same schema written out.
• CanonicalSchema#subtract asking for a complement where the difference is one of the operands or empty, declining on schemas it can subtract.
• Set operations keeping $defs entries the result no longer references, which then showed up in the emitted schema.
• CanonicalSchema#union declining over an approximated intersection, where the union itself is exact.