Use the same script as is used in moby/moby, which more gracefully
handles an existing `go.mod` (which can be symlinked) into account.
- keep the scripts called generic, and update the Makefile to invoke
them with the "with-go-mod.sh" script.
- use "go run" instead of building temporary binaries
- check if go-md2man exists before building a binary
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Sebastiaan van Stijn