Add mod_counter example

This is a slightly more complicated example that appears to work.  Of
course, it's not really much of a test...
Add Chisel pkg-config C++ flags

This is necessary when you're using a non-system Chisel build.
Change "reg" node semantics

I'm not entirely sure what the semantics of a "reg" node should even
be, but it appears that they've at least somewhat changed.  As far as
I can tell, the two reg arguments used to involve something related to
reset.  Now I've only generated a reg with the first argument set to
"1" -- I'm guessing it's some kind of write enable, but I guess we'll
have to see what happens...