update about us with popularity indices (en)
Fix minor links
Translate member policy of security (ko)
Fix link
Fix page anchors on installation page (en)

Use markdown for header ids instead of named anchor tags.
Fix page anchors on installation page (ja, pl)
Fix heading levels on installation page (ko)
Fix page anchors on installation page (translations)
Fix code on installation page (ko)
Emphasize first paragraph on installation page (en, ko, pl)
Fix markdown of first paragraph on mirrors page

The attribute list must follow without a leading blank line.
Merge pull request #601 from marocchino/fix-page-anchors

Fix page anchors on installation page (ja, pl)
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)