Fixed a typo. (Principle -> Principal)
Introduced NewArticleController.
Introduced the ArticleService property.
Implemented the GetAsync method.
Created PostArticleViewModel.
Implemented the PostAsync method.
Created the PutArticleViewModel class.
Implemented the PutAsync method.
Addressed missing guard clauses.
Addressed some code-analysis errors.
Implemented the DeleteAsync method.
Merge branch 'get-new-articles'