Updated Guidelines Draft

[Bohuslav Kabrda]

Hi guys,
thank you all for your comments. I updated the guidelines draft to reflect them:
- BR: ruby is now replaced with BR: ruby-devel for Ruby packages.
- The Gem versioned dependencies for R: and BR: were reformulated.
- Examples for packaging Gems with C extensions (did some rewriting in that section, too) and packaging Ruby applications (also fixed the header from h3 to h2 here :)) were added.
- Creation of non-Gem subpackages is no longer allowed.

It would be great if you could comment on the changes.

Regards,
Bohuslav.