Localized

[rofinn]

Closes #121

• Replaced ZonedDateTime w/ Localized{<:AbstractDateTime}
• We didn't need Localized/ZonedDateTime inner constructors, so turned them to outer constructors.
• Renamed all variable references of zdt with ldt
• Renamed '2' conversion methods to use localized rather than zdt

[omus]

Thanks for the PR. I think we should sit on this for a little while as I'd like to experiment with Localized{Date} and Localized{Time} to avoid too much churn. Having a parameterized Localized type will allow us to support higher-accuracy instant types which will be much more compossible with other packages.