C++17: [[fallthrough]] Attribute

C++17 added the [[fallthrough]] attribute to help protect against forgetting a break statement in a case statement. If a break is missing and the [[fallthrough]] attribute is not given then a warning may be given by the compiler.  MSVS 2017 does not handle this attribute.

References:

https://en.wikipedia.org/wiki/C%2B%2B17

https://infektor.net/posts/2017-01-19-using-cpp17-attributes-today.html