Encourage users to install the ruby-full meta-package.

* This will also install ruby-dev, which is needed for compiling any C
  extensions.
Emphasis installing ruby from the package manager.

* Most users just need a Ruby so they can run sass or jekyll.
  Whereas RVM/rbenv are more suited for developers and power-users.
Organize in-page links by installation method than by platform/tool.

* Combined the Package Management Systems sub-list into the top list.
Split the "Third party tools" section into "Installers" and "Managers".
Added ruby-build and ruby-install to the Installers section.
Added chruby to the Managers section.
Put Installers before Managers.
Add a summary to the Installers section.
Link to the chruby section.
Note on 'ruby-install'

Added section about ruby-install.
Update Ruby-forum.org --> Ruby-forum.com and more (pt)
Fix small typo and Archives references (pt)
Fix Documentation Archives link (pt)
Add comp.lang.ruby Newsgroup line (pt)
Fix links to Ruby-PT group (pt)
Add note refering to lists.ruby-lang.org (pt)
Add emphasis on 'controller address' (pt)
Add alert about not using HTML e-mail (pt)
Fix small typo in _config.yml (pt)
Add languages_heading (pt)