Add a dummy version of the VCD dumper

This doesn't actually compute any values for a circuit, but it does at
least write out a header file and do a bunch of name mangling
correctly.
Ignore generated Torture files
Dump VCD values

This required a whole bunch of setup.  Specifically, I had to make
patterns capable of generating values for their outputs, which was the
hardest thing to do.

I'm using GMP to support multi-precision arithmetic.