update about us with popularity indices (en)
Fix minor links
Translate member policy of security (ko)
Fix news post title and time format; rewrap
Merge pull request #516 from mtylty/update-tiobe-about-us

update about us with popularity indices (en)
Small fixes on security page (en, ja, pl)

Change 'ruby' to 'Ruby', 'CRuby' to 'MRI'.
Fix typo (pl)
Fix typo
Fix typos
Small changes on downloads page (en)

Typos, style, markdown.
Sync markdown of downloads page to en (ja, ko, pl)
Fix Linux/UNIX and OS X on installation page
Unify markdown of installation page
Remove unused page anchors on installation page
Review installation page (en)

Fix typos and style; also make minor content changes (summary).
Unify OS words (ko)
Translate RailsInstaller and Ruby Stack (ko)
Update about us with popularity indices (ko)
Add `Editors and IDEs` section (ja)
Use link reference numbers of English page, and rename duplicated references in Japanese page