Add a VersionConstraint.union() method and a new VersionConstraint.unionOf() constructor. These each return a constraint that matches multiple existing constraints.
Add a VersionConstraint.allowsAll() method, which returns whether one constraint is a superset of another.
Add a VersionConstraint.allowsAny() method, which returns whether one constraint overlaps another.
Version now implements VersionRange.
Add support for the ^ operator for compatible versions according to pub's notion of compatibility. ^1.2.3 is equivalent to >=1.2.3 <2.0.0; ^0.1.2 is equivalent to >=0.1.2 <0.2.0.
Add Version.nextBreaking, which returns the next version that introduces breaking changes after a given version.
Add new VersionConstraint.compatibleWith(), which returns a range covering all versions compatible with a given version.
Add a custom VersionRange.hashCode to make it properly hashable.