=== ICALToJsonAttribute

ICALToJsonAttribute takes a map of ICAL4J objects attached as attribute, and
output the map of corresponding json bytes as an other attribute, with unique String keys.

The JSON contains the following fields :

* *ical* : the raw ical string, in UTF-8
* *sender* : the sender of the mail (compulsory, mail without sender will be discarded)
* *recipient* : the recipient of the mail. If the mail have several recipients, each recipient will have its own JSON.
* *uid* : the UID of the ical (optional)
* *sequence* : the sequence of the ical (optional)
* *dtstamp* : the date stamp of the ical (optional)
* *method* : the method of the ical (optional)
* *recurrence-id* : the recurrence-id of the ical (optional)

Example are included in test call ICalToJsonAttributeTest.

Configuration example :

....
<mailet match=??? class=ICALToJsonAttribute>
    <sourceAttribute>icalendars</sourceAttribute>
    <destinationAttribute>icalendarJson</destinationAttribute>
</mailet>
....