Part 1 of inlining Subsystem::Guts implementation, which profiling showed was using a significant amount of time. Here I have gotten rid of Subsystem::Guts::GutsRep and incorporated its data and methods directly into Subsystem::Guts, with many methods inlined. There are still a large number of frequently-used methods that haven't been inlined yet.
Finish inlining Subsystem class, including the rest of Subsystem::Guts and the Subsystem handle class. So far this has not resulted in any speedup in Visual Studio 2013 and in fact seems to be a little slower. But I'm plowing forward with it anyway since other optimizations are enabled by inlining here (and other compilers may handle it better).
Some doxygen tweaks.