Patterns and specifiers for OffsetDateTime

[GoogleCodeExporter]

OffsetDateTime does not support a formatting and parsing pattern.

One of the issues is that OffsetPattern shares specifiers with LocalTime.  I 
suggest we add 'z' specifier to OffsetPattern to handle the Offset, ala 
http://msdn.microsoft.com/en-us/library/8kb3ddd4.aspx#zzzSpecifier 

Allow a 'zzzz', which includes fractional seconds. e.g. '-07:00.1'.

Allow a 'Z', 'ZZ', 'ZZZ', 'ZZZZ', which uses 'Z' for '+00:00' and '-00:00'.

An OffsetDateTimePattern can then be added.  It uses all the LocalDateTime 
specifiers plus the Z/z's from OffsetPattern.

Original issue reported on code.google.com by makaretu on 4 Nov 2012 at 1:21