* add configuration for missing_docs
* fix MissingDocsRuleConfiguration
* add to changelog
* fix up Config default values and update tests
* use XCTAssertTrue and XCTAssertFalse
* fix line length violation
* finish up unit tests
* rever Package.resolved
* `excludes_extensions` defaults to `true` to skip reporting violations
for extensions with missing documentation comments.
* `excludes_inherited_types` defaults to `true` to skip reporting
violations for inherited declarations, like subclass overrides.