Added --listings-env option to allow settings the name of the code block environment when using listings.
This allow using a template with \lstnewenvironment for settings a custom environment.
I tested manually and with test-pandoc and everything passed
Added --listings-env options for specifying environment name for list…
Might also want to consider an example of how to use it in the template perhaps? Or docs.
Good point @jamtur01 but I am not sure about where to do that, if @jgm decide to accept this pull request I'll consult with him about the best way (maybe as an example or in the User guide on the website)