add sub-menus, menus tag visibility about matfortytwo

[francescodist]

Hi Jean,
thanks for opening this issue. I have an idea on how to deal with sub-menus. Regarding the second request, could you add more detail? It could be worth to open a separate issue for the second point

[francescodist]

@jeanvdr I opened a PR ( #23 ) for this issue. Let me know what you think about it

[francescodist]

basically when you generate a nav page (-n) you can add a -g (--group) parameter to set a group for that page. The pages will be grouped in the sidenav using this value (which will also be the title shown for the group). Since this is also going to be the title, values with spaces are allowed, but you will need to use quotes.
E.G.
npm run genpage -- -n child-one -g 'group one'

[jeanvdr]

this is very, very nicely and effectively done !
a -t option for page's title (different from page's name) in genpage script would also be nice
Thanks +++