add example for reading packages, fix functions return pointers to copy on stack

src/commands/bitvec_command.rs

@@ -65,7 +65,7 @@ pub unsafe extern "C" fn sp_cmd_bitvec_free(command: NonNull<BitVecCommand>) {
 pub unsafe extern "C" fn sp_cmd_bitvec_get(
     mut command: NonNull<BitVecCommand>,
 ) -> *mut DisplayBitVec {
-    &mut unsafe { command.as_mut() }.bitvec
+    unsafe { &mut command.as_mut().bitvec }
 }
 
 /// Moves the provided [BitVec] to be contained in the [BitVecCommand].

src/commands/brightness_grid_command.rs

@@ -76,7 +76,7 @@ pub unsafe extern "C" fn sp_cmd_brightness_grid_set(
 pub unsafe extern "C" fn sp_cmd_brightness_grid_get(
     mut command: NonNull<BrightnessGridCommand>,
 ) -> *mut BrightnessGrid {
-    &mut unsafe { command.as_mut() }.grid
+    unsafe { &mut command.as_mut().grid }
 }
 
 /// Overwrites the origin field of the [BrightnessGridCommand].

src/commands/char_grid_command.rs

@@ -74,7 +74,7 @@ pub unsafe extern "C" fn sp_cmd_char_grid_set(
 pub unsafe extern "C" fn sp_cmd_char_grid_get(
     mut command: NonNull<CharGridCommand>,
 ) -> *mut CharGrid {
-    &mut unsafe { command.as_mut() }.grid
+    unsafe { &mut command.as_mut().grid }
 }
 
 /// Reads the origin field of the [CharGridCommand].

src/commands/cp437_grid_command.rs

@@ -83,7 +83,7 @@ pub unsafe extern "C" fn sp_cmd_cp437_grid_set(
 pub unsafe extern "C" fn sp_cmd_cp437_grid_get(
     mut command: NonNull<Cp437GridCommand>,
 ) -> *mut Cp437Grid {
-    &mut unsafe { command.as_mut() }.grid
+    unsafe { &mut command.as_mut().grid }
 }
 
 /// Gets the origin field of the [Cp437GridCommand].

src/commands/global_brightness_command.rs

@@ -53,5 +53,5 @@ pub unsafe extern "C" fn sp_cmd_brightness_global_set(
 pub unsafe extern "C" fn sp_cmd_brightness_global_get(
     mut command: NonNull<GlobalBrightnessCommand>,
 ) -> *mut Brightness {
-    &mut unsafe { command.as_mut() }.brightness
+    unsafe { &mut command.as_mut().brightness }
 }