Draft of long article on error handling and Futures.

BUG=

Review URL: https://chromiumcodereview.appspot.com//12228002
Convert to markdown, add more topics.

Staged at: http://html-streams.dart-lang.appspot.com/articles/improving-the-dom/

Review URL: https://chromiumcodereview.appspot.com//12537015
Add tutorials more prominently to front page

Staged at:

http://frontpage.dart-lang.appspot.com/

Review URL: https://chromiumcodereview.appspot.com/12589006
typo fix with code example
Update two figures

BUG=9052

Review URL: https://chromiumcodereview.appspot.com/12642009
add simd preso

BUG=

Review URL: https://chromiumcodereview.appspot.com//12531005
Merge pull request #39 from financeCoding/futures-and-error-handling-typo

typo fix with code example in futures-and-error-handling
add more samples
convert to markdown

staged at http://idiomatic.dart-lang.appspot.com/articles/idiomatic-dart/

Review URL: https://chromiumcodereview.appspot.com//12806003
Minor fixes.

Future.delayed calls updated.
Link to other Futures articles no longer absolute.

BUG=

Review URL: https://chromiumcodereview.appspot.com//12540004
update some book figures

Review URL: https://chromiumcodereview.appspot.com/12632019
move dart-web-components to web-ui; remove duplicate dart2js and dart-vm pages

Also general link cleanup. Staged at:

http://webui.dart-lang.appspot.com/

BUG=8105

Review URL: https://chromiumcodereview.appspot.com/12615008
Merge branch 'string_recipes' of https://github.com/dart-lang/dartlang.org into string_recipes
Moved index.markdown file containing string recipes.

The index.markdown file is a generated doc.  The original can be read at:
https://github.com/dart-lang/cookbook/blob/scripts/book.asciidoc

The script for converting asciidoc to markdown can be read at:
https://github.com/dart-lang/cookbook/blob/scripts/format_for_dartlang.dart.