unity::Exception's what() implementation makes debugging difficult

unity::Exception says that subclasses should implement what() such that it returns the name of the exception, which means that code that prints exceptions without using the special to_string() method omits the reason string.

For example, an uncaught exception from a GTest test will display as:

    terminate called after throwing an instance of 'unity::api::scopes::MiddlewareException'
      what(): unity::api::scopes::MiddlewareException

Is there any reason why we couldn't have unity::Exception implement what() to return the "reason" string, and not have subclasses override it? The docs say that the return value of what() is only required to be valid while the exception is valid, so using reason_.c_str() should be safe.