Fix component documentation for bmqt_subscription

Currently, [the component-level documentation for
`bmqt_subscription`][bmqt_subscription] references
`bmqt::Subscription_Handle` and `bmqt::Subscription_Expression`
classes, which do not exist.  This results in broken links within our
published documentation.  This patch corrects the documentation
comment to correctly reference `bmqt::SubscriptionHandle` and
`bmqt::SubscriptionExpression`, respectively.

[bmqt_subscription]: https://bloomberg.github.io/blazingmq/docs/apidocs/cpp_apidocs/group__bmqt__subscription.html

Signed-off-by: Patrick M. Niedzielski <patrick@pniedzielski.net>

src/groups/bmq/bmqt/bmqt_subscription.h

@@ -20,8 +20,8 @@
 //@PURPOSE: Provide a value-semantic types for subscription related API.
 //
 //@CLASSES:
-//  bmqt::Subscription_Handle:      uniquely identifies Subscription
-//  bmqt::Subscription_Expression:  Subscription criteria
+//  bmqt::SubscriptionHandle:       uniquely identifies Subscription
+//  bmqt::SubscriptionExpression:   Subscription criteria
 //  bmqt::Subscription:             Subscription parameters
 //
 //@DESCRIPTION: 'bmqt::Subscription' provides a value-semantic type carried