Produce the documentations in man .1 and markdown formats.
The template for markdown was patched to removed column "Environment variables"
Upstream PR: https://github.com/urfave/cli-docs/pull/15
Also the input has to be pre-processed to remove nested "help" subcommands from
each subcommand to improve readability.
Upstream PR: https://github.com/urfave/cli-docs/pull/16