stdlib: Implement (scheme time)

This makes a very lazy attempt at implementing TAI for (current-second).
It will first try CLOCK_TAI if available and then fall back to
CLOCK_REALTIME with a fixed offset. CLOCK_TAI is Linux-specific and
unexposed by glibc so this won't work without manual hacking.

(current-jiffy) is implemented as CLOCK_MONOTONIC and falls back to
CLOCK_REALTIME if that's not available.

On Mac OS X clock_gettime() is unsupported so gettimeofday() is used
instead. Unfortunately this only have microsecond resolution.
stdlib: Implement (command-line)

- Pass argc and argv to lliby_init() and have init.cpp stash the values
  away. This could theoretically be per-world which would allow better
  "virtualisation" of worlds. However, without a specific use case this
  isn't worth the complexity or per-world overhead

- Expose the command line arguments to the rest of the runtime as
  lliby::commandLineArguments()

- Implement (command-line) on top of commandLineArguments()