Add a tracing build flag

[harendra-kumar]

In some cases, especially for parser drivers, it would be useful to print what is happening for better debugging. We have a DEBUG flag but that is to enable debugging to find problems during production deployments. The tracing would be more for development time issues.

trace/traceM are found to be useless in Parser driver debugging, we do not see most of the prints at all! So we can use MonadIO constraint and putStrLn under the TRACE flag for tracing.