Integrate and test help2man support

[tmpfs]

Currently, the help output works nicely with help2man with the exception that the titles 'Options:' and 'Commands:' do not work well in the generated man page, an environment variable can be added to disable printing these titles as well as a configuration option.

Once commands can be built in a tree structure then the ability to add a man page per command would also be useful.

[tmpfs]

Control of help titles added in 9982566.

[tmpfs]

Support for environment variable override added in f66f678.

[tmpfs]

Support printing help as JSON than the cli tool for generating man pages climan(1) (yet to be implemented) needn't depend upon help2man.

This could be controlled with the environment variable CLI_TOOLKIT_HELP_JSON.

[tmpfs]

Patches for help2man for better section and subsection handling: https://github.com/freeformsystems/help2man