Text.Pandoc.App.CommandLineOptions and pandoc-cli/src/pandoc.hs
had similar code for generating version information.
To avoid duplication, we now export `versionInfo` from
Text.Pandoc.App [API change]. (The function is reexported from the
non-public module Text.Pandoc.App.CommandLineOptions.) This function
has three parameters that can be filled in when it is called by
pandoc-cli.
This change will make it simpler to revise version information.
John MacFarlane
ee4c9352ee