vpi_get_str() can now return a reasonable value for most of the
types used in vvp. I'm not certain I got all of them, but they
are easy to add if any are missing. I also fixed a couple of
typos that I found while looking for all the different types.
scaled to the local units. Change the internal
implementation of vpiSystemTime the $time functions
to properly account for this. Also add $simtime
to get the simulation time.