Documentation fix to avoid warnings from clang

https://releases.llvm.org/8.0.0/tools/clang/docs/DiagnosticsReference.html#id190

Author: sean-parent

include/stlab/enum_ops.hpp

@@ -80,11 +80,12 @@ auto stlab_enable_bitmask_enum(...) -> std::false_type;
 /// operators.
 auto stlab_enable_arithmetic_enum(...) -> std::false_type;
 
-/// @{
-/// \deprecated Use stlab_enable_bitmask_enum and stlab_enable_arithmetic_enum instead.
+// Don't use the `\ deprecated` Doxygen tag here because clang will warn that the
+// documentation marks the operations deprecated but the deprecated attribute is missing.
+/// \note Use is **deprecated**. Use stlab_enable_bitmask_enum instead.
 auto adobe_enable_bitmask_enum(...) -> std::false_type;
+/// \note Use is **deprecated**. Use stlab_enable_arithmetic_enum instead.
 auto adobe_enable_arithmetic_enum(...) -> std::false_type;
-/// @}
 
 /**************************************************************************************************/