Refactor the chrono cast functions into chrono.h.
Add unit tests and documentation for the chrono cast.
diff --git a/docs/basics.rst b/docs/basics.rst
index 3e07e0e..339d559 100644
--- a/docs/basics.rst
+++ b/docs/basics.rst
@@ -297,6 +297,10 @@
+---------------------------------+--------------------------+-------------------------------+
| ``std::function<...>`` | STL polymorphic function | :file:`pybind11/functional.h` |
+---------------------------------+--------------------------+-------------------------------+
+| ``std::chrono::duration<...>`` | STL time duration | :file:`pybind11/chrono.h` |
++---------------------------------+--------------------------+-------------------------------+
+| ``std::chrono::time_point<...>``| STL date/time | :file:`pybind11/chrono.h` |
++---------------------------------+--------------------------+-------------------------------+
| ``Eigen::Matrix<...>`` | Eigen: dense matrix | :file:`pybind11/eigen.h` |
+---------------------------------+--------------------------+-------------------------------+
| ``Eigen::Map<...>`` | Eigen: mapped memory | :file:`pybind11/eigen.h` |