Command: major code refactoring

ditto; and multi-command support was removed in favor of JSON config
support

src/modules/command/command.h

@@ -0,0 +1,9 @@
+#pragma once
+
+#include "fastfetch.h"
+#include "modules/command/option.h"
+
+void ffPrintCommand(FFinstance* instance, FFCommandOptions* options);
+void ffInitCommandOptions(FFCommandOptions* options);
+bool ffParseCommandCommandOptions(FFCommandOptions* options, const char* key, const char* value);
+void ffDestroyCommandOptions(FFCommandOptions* options);