Add a script to synchronize with CalDAV servers

Introduce calcurse-caldav, a Python script that can be used to
synchronize calcurse instances with CalDAV servers.

The script was tested with an instance of the Radicale CalDAV server but
it is still alpha software. Make backups before giving it a try!

Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

contrib/caldav/config.sample

@@ -0,0 +1,31 @@
+# If you want to synchronize calcurse with a CalDAV server using
+# calcurse-caldav, create a new directory ~/.calcurse/caldav/, copy this file
+# to ~/.calcurse/caldav/config and adjust the configuration below.
+
+[General]
+# Path to the calcurse binary that is used for importing/exporting items.
+Binary = calcurse
+
+# Host name of the server that hosts CalDAV.
+Hostname = some.hostname.com
+
+# Path to the CalDAV calendar on the host specified above.
+Path = /path/to/calendar/on/the/server/
+
+# Enable this if you want to skip SSL certificate checks.
+InsecureSSL = No
+
+# Disable this option to actually enable synchronization. If it is enabled,
+# nothing is actually written to the server or to the local data files. If you
+# combine DryRun = Yes with Verbose = Yes, you get a log of what would have
+# happened with this option disabled.
+DryRun = Yes
+
+# Enable this if you want detailed logs written to stdout.
+Verbose = Yes
+
+# Credentials for HTTP Basic Authentication. Leave this commented out if you do
+# not want to use authentication.
+#[Auth]
+#Username = user
+#Password = pass