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Closes #14
Rule for by-name right associative operators

Warnings for the issue presented in SI-1980:
https://issues.scala-lang.org/browse/SI-1980
Rule for PackageObjectClasses

Warnings for the issue presented in SI-4344:
https://issues.scala-lang.org/browse/SI-4344
Merge branch 'packageobjectclasses'
Rule for PackageObjectClasses

Warnings for the issue presented in SI-4344:
https://issues.scala-lang.org/browse/SI-4344
Merge branch 'packageobjectclasses'

Conflicts:
	wiki/core-rules.md
Move NullaryUnit to core
Documentation for NullaryUnit

And fixed some dead links