Generate VCD file for each cover statement

[ShashankVM]

Fixes #1287

[ShashankVM]

Hi Project Maintainers!

I've been using EBMC for hobby projects for a year now. The VCD file generation for each cover statement was a feature that I sorely missed in my projects.

I've implemented this feature and verified it is working locally. I've attached the screenshot of the results.

I'm looking forward to contributing to this project and welcome feedback!

[kroening]

This regresses on the current behavior, where you can get the trace in a file named as the argument of --vcd. The user still needs to give an argument to the --vcd switch, which will be ignored.

[ShashankVM]

Thanks for your feedback. @kroening

Do we want to keep the argument for VCD filename?

If yes, I can include the filename argument as a suffix in the final filename.

If not, I can work on modifying the command line parsing logic. Please let me know how to proceed.