Tidying (#150)

create resources folder during project_setup, and link with emscripten

--embed-file complained b/c the directory was empty, so I added
resources/placeholder.txt

I tested project_setup.sh (but not project_setup.ps1) -- the emscripten
build works

also, s/std.builtin.Mode/std.builtin.OptimizeMode
(std.builtin.Mode's source says: "///Deprecated; use OptimizeMode.")

project_setup.sh

@@ -33,6 +33,9 @@ pub fn build(b: *std.Build) !void {
 
         // Note that raylib itself is not actually added to the exe_lib output file, so it also needs to be linked with emscripten.
         const link_step = try rlz.emcc.linkWithEmscripten(b, &[_]*std.Build.Step.Compile{ exe_lib, raylib_artifact });
+        //this lets your program access files like "resources/my-image.png":
+        link_step.addArg("--embed-file");
+        link_step.addArg("resources/");
 
         b.getInstallStep().dependOn(&link_step.step);
         const run_step = try rlz.emcc.emscriptenRunStep(b);
@@ -69,4 +72,7 @@ echo '.{
 }' >> build.zig.zon
 
 mkdir src
+mkdir resources
+touch resources/placeholder.txt
+
 cp ../examples/core/basic_window.zig src/main.zig