Blackboxhelper (#418)

* First pass at implementing a annotation based mechanism to move black box verilator files into the target directory

* A little bit of style cleanup

* A little bit of style cleanup

* Fix the driver, wasn't appending targetDir properly
Add some docs

* test had wrong value now that targetdir is added to annnos

* Now saves a list of all black box verilog files moved into target directory.
Then creates a file black_box_verilog_files.f that contains this list with -v prepended to each line

* Made black box source helper be low to low form
Added it to the verilog compiler transforms
Added a test to make sure it got there

* targetDir annotation is targeted to a CircuitName("All")