Added latest news posts (pt)
Correcting translation and replacing 'Decimal' with 'Rational'
Make download links clearly
Extract installation steps to Installation page
Move alternative impls to about page
Add description about method define return value
Merge pull request #507 from DiogoAndre/latests-news-pt

Added latest news posts (pt)
Merge pull request #578 from marocchino/2.1.0-quickstart

Add description about method define return value
Fix typo
Merge pull request #576 from sorah/reorganize_download_and_installation

Extract installation steps to Installation page
Extract a page about mirror sites
Add `Ruby Referense manual Ruby 2.1.0 version` link (ja)
Merge pull request #585 from bash0C7/link_ruby_reference_manual_ruby_2.1.0_ja

Add `Ruby Referense manual Ruby 2.1.0 version` link (ja)
Fix typo (s/confortable/comfortable/g)
Merge pull request #584 from makimoto/extract-mirrors

Extract a page about mirror sites
Fix typo