Rename flo-llvm-c++ to flo-llvm-debug, add flo-llvm-release

This is a pretty major change: there are now three modes of running
flo-llvm:

* vcdtmp, which emits all nodes to the VCD file and C++ header
* debug, which emits all Chisel-named (ie, inside a module) nodes to
  the VCD file and C++ header, along with all state to the C++ header
* release, which emits only IO to the VCD file, and all state to the
  VCD file.

These three version should be sufficient for duplicating the
functionality of Chisel's C++ backend, it's now just a manner of
making everything work...