Add API to expand export / import dialog

lib/macro/macro-export-extensions.cpp

@@ -0,0 +1,17 @@
+#include "macro-export-extensions.hpp"
+
+namespace advss {
+
+static std::vector<MacroExportExtension> extensions;
+
+void AddMacroExportExtension(const MacroExportExtension &ext)
+{
+	extensions.emplace_back(ext);
+}
+
+const std::vector<MacroExportExtension> &GetMacroExportExtensions()
+{
+	return extensions;
+}
+
+} // namespace advss