Update dart:io article code samples to match changed article.
stopping tutorial sidebar from scrolling with page
adding new download button icon
increasing size of h4
Merge branch 'dart-1.0' of github.com:dart-lang/dartlang.org into dart-1
adding retina sprite css
updating minifying image
making slider buttons larger on mobile
adding padding to code samples
reverting to old Optionally Types image
partial fix for company name pop-in
Merge pull request #221 from ocupop/dart-1.0

dropped in flight school
Merge branch 'dart-1.0' of github.com:dart-lang/dartlang.org into dart-1
updating paragraph line spacing
Notice when the reader clicks "See code"

R=amjoyce@chromium.org

Review URL: https://chromiumcodereview.appspot.com/70273010
Merge pull request #222 from ocupop/dart-1.0

Fixes and copy edits
Merge branch 'dart-1.0' of github.com:dart-lang/dartlang.org into dart-1
regenerate the book, hide remarks

Review URL: https://chromiumcodereview.appspot.com/64793005
added popups to front page code snippets

BUG=

Review URL: https://chromiumcodereview.appspot.com/61693004
further work to fix company name pop-in