CLI fixes: Hpricot => Nokogiri, updates, styles

Hi,

this is a rather large pull request:

- removes Hpricot, switches to Nokogiri
- tweaks some styles
- bumps dependencies as far as nothing breaks
- compatibility changed to >= 1.9.3 incl. JRuby

I would also volunteer to maintain the gem on rubygems, if this is acceptable to you.