This change adds `--man1` and `--man5` options to pandoc, so
pandoc can generate its own man pages.
It removes the old overly complex method of building a separate
executable (but not installing it) just to create the man pages.
The man pages are no longer automatically created in the build
process.
The man/ directory has been removed. The man page templates
have been moved to data/.
New unexported module: Text.Pandoc.ManPages.
Text.Pandoc.Data now exports readmeFile, and `readDataFile`
knows how to find README.
Closes#2190.
fe625e053d