mach: fundamental changes

- Core doesn't depend to `App` anymore
 - `setOptions` has replaced with some new functions (`setTitle`,
   `setSize`, etc)
   - and more

src/Timer.zig

@@ -1,20 +1,20 @@
 const std = @import("std");
 const platform = @import("platform.zig");
 
-const Timer = @This();
+pub const Timer = @This();
 
-backing_timer: platform.BackingTimerType = undefined,
+internal: platform.Timer,
 
 /// Initialize the timer.
 pub fn start() !Timer {
     return Timer{
-        .backing_timer = try platform.BackingTimerType.start(),
+        .internal = try platform.Timer.start(),
     };
 }
 
 /// Reads the timer value since start or the last reset in nanoseconds.
 pub inline fn readPrecise(timer: *Timer) u64 {
-    return timer.backing_timer.read();
+    return timer.internal.read();
 }
 
 /// Reads the timer value since start or the last reset in seconds.
@@ -24,12 +24,12 @@ pub inline fn read(timer: *Timer) f32 {
 
 /// Resets the timer value to 0/now.
 pub inline fn reset(timer: *Timer) void {
-    timer.backing_timer.reset();
+    timer.internal.reset();
 }
 
 /// Returns the current value of the timer in nanoseconds, then resets it.
 pub inline fn lapPrecise(timer: *Timer) u64 {
-    return timer.backing_timer.lap();
+    return timer.internal.lap();
 }
 
 /// Returns the current value of the timer in seconds, then resets it.