Add support for printing system time

[chtenb]

In ChucK, all the timing is relative to the time the process started. This makes it hard to track down latency problems when communicating with other programs, as is motivated by this thread in the mailing list: https://lists.cs.princeton.edu/pipermail/chuck-users/2016-May/008065.html

So here is the feature request:

• Add native support to work with the system time (just printing it would be a great start)