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.
Added Tropical Ruby 2015 CFP news (en).
Merge pull request #888 from guiocavalcanti/tropicalrb-2015

Added Tropical Ruby 2015 CFP news (en).
Rewrap news post (en)
Translate tropicalrb 2015 CFP (zh_tw).
Translate CFP for Tropical Ruby news (es)
Fix link
Merge pull request #889 from dabit/master

Translate CFP for Tropical Ruby news (es)
Small fixes (es)
Tropical ruby 2015 (ru)
Merge pull request #890 from gazay/tropical_ruby

Tropical ruby 2015 (ru)
Fixed a spelling mistake in an old news (fr).