This changes the implementation of std::time::Time so it no longer
relies on high-level date/time instructions provided by the VM. Instead
of these instructions we now use an algorithm ported over from musl to
decompose a Unix timestamp. The individual parts of a Time can in turn
be used to reconstruct a Unix timestamp. The VM in turn only provides
some low level instructions to get a timestamp, the offset, and a flag
indicating if DST is active.

A side effect of this approach is that we have to implement time parsing
and formatting ourselves. While this will take some time (e.g. we need
to implement hash maps first) all if this work is necessary anyway. On
top of that both time parsing and formatting was somewhat broken when
using the "time" crate anyway. Until time parsing/formatting is
reimplemented the methods have been changed so they produce dummy data
or throw an error.