Add safety comments to public unsafe functions (#484)

- [x] Changelog updated / no changelog update needed

agb/examples/object_text_render.rs

@@ -24,7 +24,6 @@ fn entry(gba: agb::Gba) -> ! {
 fn main(mut gba: agb::Gba) -> ! {
     let (mut unmanaged, _sprites) = gba.display.object.get_unmanaged();
 
-    loop {
     let mut palette = [0x0; 16];
     palette[1] = 0xFF_FF;
     palette[2] = 0x00_FF;
@@ -95,5 +94,4 @@ fn main(mut gba: agb::Gba) -> ! {
             line_done
         );
     }
-    }
 }

agb/src/lib.rs

@@ -231,6 +231,10 @@ pub struct Gba {
 impl Gba {
     #[doc(hidden)]
     #[must_use]
+    /// # Safety
+    ///
+    /// May only be called a single time. It is not needed to call this due to
+    /// it being called internally by the [`entry`] macro.
     pub unsafe fn new_in_entry() -> Self {
         Self::single_new()
     }

agb/src/sync/mod.rs

@@ -33,6 +33,8 @@ pub fn memory_write_hint<T>(val: *mut T) {
 /// This seems to be a problem caused by Rust issue #62256:
 /// <https://github.com/rust-lang/rust/issues/62256>
 ///
+/// # Safety
+///
 /// **WARNING FOR ANYONE WHO FINDS THIS**: This implementation will *only* be
 /// correct on the GBA, and should not be used on any other platform. The GBA
 /// is very old, and has no atomics to begin with - only a main thread and