Make Tree::changed_ranges return an Iterator instead of a Vec (#437)

* Make Tree::changed_ranges return an Iterator instead of a Vec

* Remove CBufferIter.free parameter

lib/binding_rust/util.rs

@@ -0,0 +1,38 @@
+use std::os::raw::c_void;
+
+extern "C" {
+    #[link_name = "rust_tree_sitter_free"]
+    pub fn free_ptr(ptr: *mut c_void);
+}
+
+pub struct CBufferIter<T> {
+    ptr: *mut T,
+    count: usize,
+    i: usize,
+}
+
+impl<T> CBufferIter<T> {
+    pub unsafe fn new(ptr: *mut T, count: usize) -> Self {
+        Self { ptr, count, i: 0 }
+    }
+}
+
+impl<T: Copy> Iterator for CBufferIter<T> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let i = self.i;
+        self.i += 1;
+        if i >= self.count {
+            None
+        } else {
+            Some(unsafe { *self.ptr.offset(i as isize) })
+        }
+    }
+}
+
+impl<T> Drop for CBufferIter<T> {
+    fn drop(&mut self) {
+        unsafe { free_ptr(self.ptr as *mut c_void); }
+    }
+}