Commonpy

This release adds the new function `print_boxed(...)`.

Changes in this version:
* In `net(...)`, in case of a connection error, don't do exponential back-off and retry. Retry only once and then give up, because connection errors often mean the server is not available and long waits are unhelpful to callers.
* Change `net(...)` to not test if a network is available if the given destination address is on the local host. This prevents incorrectly returning `NetworkFailure` when the current host is detached from the network and the failure is actually a `ServiceFailure` (for example, if nothing is listening on the destination port on the local host).
* Add new function `on_localhost(...)`, for testing whether a given network location indicates the local host.

Note: the previous release, 1.3.10, should not have added new functions in a patch release – API changes should result in changing the minor release number, not merely the patch number. The previous release number was a mistake; it should have been 1.4.0, but since it wasn't, this release is 1.4.0.

* Add new functions `download(...)` and `download_file(...)`.

* Don't import packages `dateparser` and `validator_collection` until actually necessary, to reduce application startup times.

* Fix problems on Windows involving the interrupt handler configured by `config_interrupt(...)`. First, the internal function used did not have a signature that was correct for `win32api.SetConsoleCtrlHandler` on Windows. Second, the proper usage is to return a value, not raise an exception.

* Make `relative(...)` from `file_utils` more robust against a problem on Windows, in which Python's `os.path.relpath` generates an error when you try to use it on a network-mapped drive.