Add time zone support

Can you add a test case to verify the following formats:
* ``R/2014-10-01T150125Ztz:PST/P1D` // lower case tz
* `R/2014-10-01T150125ZTZ:PST/P1D` // naked Z(UTC) and TZ specified
* `R/2014-10-01T150125Z-0400TZ:PST/P1D` // -0400 is EDT which times zone is selected?
* `R/2014-10-01T150125TZ:PSTZ-0400/P1D` // Z following TZ
* `R/2014-10-01TZ:EDT` // TZ specified without specific time.