feat: restructure Makefile to delegate builds to script/wren.mk and output to bin/ and lib/ directories

The monolithic Makefile is replaced with a thin wrapper that invokes
script/wren.mk for each configuration. Build artifacts are now placed
in bin/ (executables) and lib/ (static/shared libraries) instead of
the project root. The .gitignore is updated accordingly, and the
getting-started documentation reflects the new output layout.

src/main.c

@@ -56,7 +56,7 @@ static char* readModule(WrenVM* vm, const char* module)
   size_t rootLength = strlen(rootDirectory);
   size_t moduleLength = strlen(module);
   size_t pathLength = rootLength + moduleLength + 5;
-  char* path = malloc(pathLength + 1);
+  char* path = (char*)malloc(pathLength + 1);
   memcpy(path, rootDirectory, rootLength);
   memcpy(path + rootLength, module, moduleLength);
   memcpy(path + rootLength + moduleLength, ".wren", 5);
@@ -107,7 +107,7 @@ static int runFile(WrenVM* vm, const char* path)
   // Use the directory where the file is as the root to resolve imports
   // relative to.
   char* lastSlash = strrchr(path, '/');
-  rootDirectory = malloc(lastSlash - path + 2);
+  rootDirectory = (char*)malloc(lastSlash - path + 2);
   memcpy(rootDirectory, path, lastSlash - path + 1);
   rootDirectory[lastSlash - path + 1] = '\0';
 

src/wren_vm.c

@@ -1208,7 +1208,7 @@ WrenInterpretResult wrenInterpret(WrenVM* vm, const char* sourcePath,
                                   const char* source)
 {
   if (strlen(sourcePath) == 0) return loadIntoCore(vm, source);
-  
+
   // TODO: Better module name.
   Value name = wrenNewString(vm, "main", 4);
   wrenPushRoot(vm, AS_OBJ(name));
@@ -1345,7 +1345,7 @@ static void defineMethod(WrenVM* vm, const char* className,
 
   // TODO: Need to be able to define methods in classes outside the core
   // module.
-  
+
   // Find or create the class to bind the method to.
   ObjModule* coreModule = getCoreModule(vm);
   int classSymbol = wrenSymbolTableFind(&coreModule->variableNames,
@@ -1460,7 +1460,7 @@ void wrenReturnString(WrenVM* vm, const char* text, int length)
 {
   ASSERT(vm->foreignCallSlot != NULL, "Must be in foreign call.");
   ASSERT(text != NULL, "String cannot be NULL.");
-  
+
   size_t size = length;
   if (length == -1) size = strlen(text);