Create html_i18n_content.js

Generate downloadable chrome.i18n messages file for location.href.
See http://developer.chrome.com/extensions/i18n.html.
Messages are based on innerText or value attribute, keyed by class attribute.
Generate downloadable HTML file with corresponding i18n-content attributes.
Generate downloadable script to initialize localized messages on load.
Move to snippets folder, add screenshot.
Improve comment wording.
Add placeholders to messages.json. Keep localized text in HTML file for round-tripping.
Resolve trivial merge conflict in comments.
Add information for html_i18n_content.
Add animated html_i18n_content.gif to show result of running html_i18n_content.js.
Add link target for html_i18n_content fragment specifier.
Revert link target change since GFM generates link targets for headings.

Eclipse Orion UI can't revert change due to Eclipse Orion Bug 417004.
Update README.md

Sanitize my wording for html_i18n_content.
Update README.md

Improve html_i18n_content wording.