Time utility

[frsechet]

Is your feature request related to a problem? Please describe.
getting the current time or converting timestamps to various formats requires using an external function, which is cumbersome, requires external code in a different programming language, requires an external Fn runtime, and adds delays. It would be useful to add some way to get timestamps, convert those in various formats, get timediffs, and optionally change timezone...

ESPECIALLY useful for calendar-types of chatbot (book an event on date X)

Describe the solution you'd like
Some inspiration:

• JS: built-in Date, date-fn, momentjs...
• rust: chrono, chrono-tz
  etc.

Describe alternatives you've considered
Fn("getTime", ...)

[frsechet]

For reference:

Time() => initialize Time obj (UTC)
Time().at(2019, 03, 28, 12, 53, 20, 123) => initialize a Time obj on 2019-03-28 at 12h53m20s.123
Time()... .unix() => Time as unix timestamp (in milliseconds)
Time()... .format() => ISO-formatted string representing the Time obj
Time()... .format("%h%d etc") => custom-formatted string representing the Time obj (see https://docs.rs/chrono/0.4.19/chrono/format/strftime/index.html)