Helpful error message in dtcw

I am trying to get `docToolchain` running for my project. In the process of wrapping my head around things, I have experienced somewhat a lack of helpful error messages in `dtcw`.

For instance, it would be awesome, if the config file `docToolchainConfig.groovy` could be sanity checked. I am thinking of checking whether the `inputPath`, `inputFiles`, `imageDirs`, etc. have been set and the paths actually exist on disk.

Currently, when those are wrongly set, `dtcw` just silently does nothing and it is hard to see what is going on. It would be cool to have some hints on what is going on.