ZonedDateTime formatting and support for time zone abbreviations

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Hi!

I would like to display ZonedDateTime to the user with some kind of formatting 
and info of the timezone.

Currently calling ToString() on a ZonedDateTime yields something like this 
(es-ES Culture) in Madrid.

Local: 25/04/2013 11:50 Offset: +02 Zone: Europe/Paris

It would be nice to:

1) Give ZonedDateTime better ToString support as other Noda types have
2) Support standard/daylight/summer abbreviations in the 
formatting. (I think this info is in the tz database sources, but NodaTime 
currently doesnt seem to use it)
3) Make reasonably formatting defaults for a ZonedDateTime including the 
systems culture (for example show CET in culture "es-ES" but MEZ if culture 
"de-DE")

Formatting examples:
25/04/2013 11:50 CEST
25/04/2013 11:50 MESZ
25/04/2013 11:50 CEST (UTC+2)
25/04/2013 11:50 UTC+02

I suppose this is a very low priority item, as the user generally does not care 
about their timezone abbreviation, but it may be useful to give feedback to the 
user that this is ZonedDateTime according to a time zone, specially when you 
want to display a ZonedDateTime that originates in a different timezone that 
the one the user is on.

I think that the OffsetDateTime formatting can also be improved.

Germán

Original issue reported on code.google.com by germanft...@gmail.com on 25 Apr 2013 at 10:33