Support for non-constant timezones

[pineapplemachine]

See https://en.wikipedia.org/wiki/Tz_database

Currently the only named timezones that strtime supports are those that have a constant offset, e.g. "UTC" or "EEST". The package should not itself contain data regarding timezones like "America/New_York", "Europe/Paris" but it should provide some way to integrate with another service or package so that these timezones can be used.

[pineapplemachine]

Noting a possible native JS resource for this functionality:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl