Re-organise external-facing headers to be more easily used

* renderdoc/api/replay/ contains all the headers for using the replay and
  analysis side of renderdoc (like in a UI or auto-testing tool)
* renderdoc/api/app/ contains the headers if you wanted to write a
  renderdoc-aware application.

renderdoccmd/renderdoccmd.cpp

@@ -24,7 +24,8 @@
 
 #include <string>
 
-#include <replay/renderdoc.h>
+#include <replay/renderdoc_replay.h>
+#include <app/renderdoc_app.h>
 
 using std::string;
 using std::wstring;