Add Help page with generated markdown output for all commands and topics

[mgrojo]

This goes with alire-project/alire#1464

[mgrojo]

Example of the presentation:

[mgrojo]

By the way, to make Jekyll to work I have to add this change:

@ -29,5 +29,6 @@ install_if -> { RUBY_PLATFORM =~ %r!mingw|mswin|java! } do
 end
 
 # Performance-booster for watching directories on Windows
 gem "wdm", "~> 0.1.0", :install_if => Gem.win_platform?
 
+gem "webrick"

I suppose it's something related to different versions of the gems or of something else. I've not added it because it was needed before my changes.

[mgrojo]

Update with the related pull requests in alire and clic.