Separate temporal interface layer

The only remaining connection between the temporal interfaces and the chrono intrefaces or concrete classes is the definition of resolve on TemporalField. If this is changed from zone and chronology to be TemporalAccessor, the separation can be complete.

The JDK implementations can use package scoped methods to avoid any performance loss.

See also JSR 301 issue https://github.com/ThreeTen/threeten/issues/341