Function imgui_sys::igSetAllocatorFunctions

pub unsafe extern "C" fn igSetAllocatorFunctions(
    alloc_func: Option<unsafe extern "C" fn(sz: usize, user_data: *mut c_void) -> *mut c_void>, 
    free_func: Option<unsafe extern "C" fn(ptr: *mut c_void, user_data: *mut c_void)>, 
    user_data: *mut c_void
)