Create a class for deferred error logging (#390)

## Link to GitHub Issue, if one exists
#388 

## Description of change
Instead of setting flags in `signal` and logging when we crash, create a
class for logging deferred semi-fatal messages, and dump them to the log
immediately before crashing or shutting down.

## Testing
Tested each failure case by injection.

src/spice2x/util/deferlog.h

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <string>
+#include <vector>
+#include <initializer_list>
+
+namespace deferredlogs {
+
+    // some shared error messages
+    extern const std::initializer_list<std::string> SUPERSTEP_SOUND_ERROR_MESSAGE;
+
+    void defer_error_messages(std::initializer_list<std::string> messages);
+    void dump_to_logger();
+}