add back dot and svg export

[mschoch]

I removed the dot and svg export code while making substantial improvements to the build phase.

The previous implementations would only work with the Builder, not the final FST. The new implementations will only work with the final FST (out of the box) and not with the Builder. The reason is that the builder no longer has direct access to everything required. It only has the unfinished nodes (stack) and registry of frequently used nodes. All other nodes that have been flushed out are forgotten by the builder (by design).

Exporting of the final FST to dot/svg will be exposed through the cmd-line tool, and at least initially function much like the debug command.