Add fatal errors.

Errors are fatal if the program has to stop immediately.

src/log.cpp

@@ -63,6 +63,7 @@ void init()
                              keywords::format =
                                  "%LineID% [%TimeStamp%] "
                                  "[%ThreadID%]: [%Severity%] %Message%");
+
     boost::log::add_console_log(std::cerr,
                                 keywords::format = translate("WARNING").str()
                                                    + ": %Message%")
@@ -71,6 +72,11 @@ void init()
                                 keywords::format = translate("ERROR").str()
                                                    + ": %Message%")
         ->set_filter(boost::log::trivial::severity == sev::error);
+    boost::log::add_console_log(std::cerr,
+                                keywords::format = translate("FATAL ERROR")
+                                                       .str()
+                                                   + ": %Message%")
+        ->set_filter(boost::log::trivial::severity == sev::fatal);
 
     boost::log::add_common_attributes();
 }

src/main.cpp

@@ -76,7 +76,7 @@ int main(int argc, char *argv[])
     }
     catch (std::exception &e)
     { // Exceptions we can't recover from or ones we don't know.
-        LOG(lg, log::sev::error)
+        LOG(lg, log::sev::fatal)
             << e.what() << translate(" (while parsing options)");
         return EXIT_FAILURE;
     }