Refactored to use itertools

Found an itertools mechanism that works for iterating
through the current and next row in the cursor.

sqlite_utils/utils.py

@@ -1,28 +0,0 @@
-def iter_pairs(iterator):
-    # Yields (item, next_item, is_last) pairs
-    # Last row is (item, None, True)
-    first = True
-    next_item = None
-    while True:
-        next_done = False
-        if first:
-            item, done = next_with_done(iterator)
-            if done:
-                break
-            next_item, next_done = next_with_done(iterator)
-            first = False
-        else:
-            item = next_item
-            next_item, next_done = next_with_done(iterator)
-
-        yield item, next_item, next_done
-
-        if next_done:
-            break
-
-
-def next_with_done(iterator):
-    try:
-        return next(iterator), False
-    except StopIteration:
-        return None, True