Add Time Zone Support

[d42ohpaz]

For localdatetime and localtime, it would be beneficial to be able to pass in an arbitrary time zone. Setting the time zone globally using date_default_timezone_set won't work, because this affects all date processing globally in PHP. The time zone only needs to be applied when using localdatetime and localtime. Thank you.

[jasny]

I will not implement this, but I'll accept PRs to solve this issue.