Diagnostics

- Added new 'diagnostics' command to assist with bug reporting,
  testing.  It answers questions such as "did you compile it yourself?",
  and more.
- Specifically, it runs a UUID generation test to prove that the UUIDs
  are really unique.

src/main.h

@@ -92,6 +92,9 @@ int deltaTags (Task&);
 int deltaAttributes (Task&);
 int deltaSubstitutions (Task&);
 
+// diag.cpp
+void handleDiagnostics (std::string&);
+
 // edit.cpp
 int handleEdit (std::string&);