Add `Create_Continue_Trace_Log` ini setting and `-CC` command line option.

Specifying `Create_Continue_Trace_Log=no` or `-CC` will suppress the creation of the `.pov-state` file. Note that while this may save space and even speed up simple renders, if you abort the render you will be unable to continue it later using the `Continue_Trace=yes` or `+C` options.