Improve OpenAPI docs

[DerStimmler]

closes #1

Breaking Changes:

• rename ToHttpResult method to ToStatusCodeHttpResult
• rename ToHttpResult<T> to ToJsonHttpResult<T>
• rename ToHttpResult<T,E> to ToJsonHttpResult<T,E>
• ToNoContentHttpResult<T> returns NoContent instead of StatusCodeHttpResult
• ToNoContentHttpResult<T,E> returns NoContent instead of StatusCodeHttpResult

Changes:

• add ToOkHttpResult<T> method
• add ToOkHttpResult<T,E> method
• add ToStatusCodeHttpResult<T> method
• add ToStatusCodeHttpResult<T,E> method