make it clear how to use module system without mach.Core (remove mach.App)

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

examples/custom-renderer/main.zig

@@ -1,3 +1,4 @@
+const std = @import("std");
 const mach = @import("mach");
 
 // The global list of Mach modules registered for use in our application.
@@ -7,11 +8,18 @@ pub const modules = .{
     @import("Renderer.zig"),
 };
 
-// TODO: move this to a mach "entrypoint" zig module
+// TODO: move this to a mach "entrypoint" zig module which handles nuances like WASM requires.
 pub fn main() !void {
-    // Initialize mach core
-    try mach.core.initModule();
+    const allocator = std.heap.c_allocator;
 
-    // Main loop
-    while (try mach.core.tick()) {}
+    // Initialize module system
+    try mach.mods.init(allocator);
+
+    // Schedule .app.start to run.
+    mach.mods.schedule(.app, .start);
+
+    // Dispatch systems forever or until there are none left to dispatch. If your app uses mach.Core
+    // then this will block forever and never return.
+    const stack_space = try allocator.alloc(u8, 8 * 1024 * 1024);
+    try mach.mods.dispatch(stack_space, .{});
 }