refactor(furvm): improve functions

Define native functions inside the module instead of the function
itself (native functions hold only the key to the definition), introduce
private functions, add parameter count to function and fix some bugs.

Closes: #20
Closes: #25

furvm/src/module.cpp

@@ -12,9 +12,10 @@ std::ostream& mod::serialize(std::ostream& os) const {
     detail::serialize(os, std::uint32_t(0)); // version
 
     detail::serialize(os, function_id(m_functionMap.size()));
-    for (const auto& [name, id] : m_functionMap) {
-        detail::serialize(os, name);
-        function_h func = m_functions.at(id);
+    for (auto* pair : m_functions) {
+        function_h func     = { pair };
+        bool       isPublic = m_publicFunctions.find(func->name()) != m_publicFunctions.end();
+        detail::serialize(os, isPublic ? func->name() : ""); // private functions have empty names
         detail::serialize(os, std::uint8_t(func->type()));
         switch (func->type()) {
         case function_t::Normal: {