improve plugin facing api with c++ helpers

solanaceae/plugin/version_helper.inl

@@ -0,0 +1,25 @@
+#pragma once
+
+namespace internal {
+	template<typename T>
+	class g_type_version {
+		typedef char yes[1];
+		typedef char no [2];
+
+		template<typename C> static yes& test_version(decltype(&C::version));
+		template<typename C> static no& test_version(...);
+
+		static bool const has_version = sizeof(test_version<T>(nullptr)) == sizeof(yes);
+		static constexpr const char* get_version(void) {
+			if constexpr (has_version) {
+				return T::version;
+			} else {
+				return "UNK"; // default version
+			}
+		}
+
+		public:
+			static constexpr const char* version = get_version();
+	};
+} // internal
+