Log Message:
py-dialog: updated to 3.5.2

Release 3.5.2

Update ChangeLog.init (improve some log messages)

demo: add example of an msgbox with timeout

* examples/demo.py: add method MyApp.timeout_demo(), which shows how to
detect a timeout when an msgbox has been presented to the user.

Fix related to the 'timeout' option (--timeout for dialog)

* dialog.py (Dialog._perform): ignore the dialog output when a timeout
occurred, which we know thanks to the exit code. Without this change,
output parsing or checking (e.g., in Dialog._widget_with_no_output())
would be broken by the '\ntimeout\n' string printed by dialog in such
cases (seen with msgbox, at least).

It might be that parsing is still disturbed for some widgets when a
timeout occurs, if they never produce an empty output in a no-timeout
situation: this remains to be checked. Also, it appears that the
--timeout option doesn't work with all widgets in the dialog
backend (tested with dialog 1.3-20201126: 'msgbox', 'checklist' and
'menu' support --timeout; 'inputbox' and 'mixedform' don't; other
widgets untested with this option).

Show use of d.add_persistent_args(["--no-nl-expand"]) in examples

* Using this option is quite relevant when using pythondialog. Thanks to
ChristianTacke for the report. Closes:
<https://github.com/frougon/pythondialog/issues/8>.

Improve support for the --timeout dialog option

* Set DIALOG_TIMEOUT in the environment when invoking dialog; this
allows us to distinguish between DIALOG_TIMEOUT and DIALOG_ESC. Add
the corresponding TIMEOUT attribute to the Dialog class.