implemented Flatten Module (#149)

* implemented flatten op

---------

Co-authored-by: Awni Hannun <awni@apple.com>

python/src/array.cpp

@@ -728,6 +728,21 @@ void init_array(py::module_& m) {
             return power(a, to_array(v, a.dtype()));
           },
           "other"_a)
+      .def(
+          "flatten",
+          [](const array& a,
+             int start_axis,
+             int end_axis,
+             const StreamOrDevice& s) {
+            return flatten(a, start_axis, end_axis);
+          },
+          "start_axis"_a = 0,
+          "end_axis"_a = -1,
+          py::kw_only(),
+          "stream"_a = none,
+          R"pbdoc(
+            See :func:`flatten`.
+          )pbdoc")
       .def(
           "reshape",
           [](const array& a, py::args shape, StreamOrDevice s) {