Allow setting timezone attribute

[Moggers]

trafficstars

Have a case where sometimes we want to display times in local TZ, sometimes based on TZ of where the timestamp originated. I've just slapped a TZ attribute on the element and passed it through - is there particular reason this isn't in the API already before I try to upstream it? Did I fail to RTFM?

[keithamus]

Seems reasonable. PRs welcome!