Use documents with title and contents

Basic change to the example app. Now the form has a title field and a
textarea for contents, as well as a submit button.

Also removed dependency on /_utils/script/sha1.js since it didn't seem
to be used.
Implement individual document view and links

Documents can now be viewed at index.html#<id>.
The documents list contains only the titles, as links.
filter for changes to specific doc
remove old logging
Implement changes feed for document view

Documents are refreshed as changes arrive.
Implement editing and saving in document view

Currently using contentEditable for the text, with explicit "Save"
button.  Will experiment with auto-saving soon.
Implement live updates

Updates are sent one second after the last keypress.
I tried sending on every keypress, but that was too fast, and led to
update conflicts for some reason.  Probably the updated ids from each
save weren't coming back fast enough.

I guess there's a hole here where you could write for hours without ever
taking a one-second break, and your work won't be saved.  We could add
alternate savers to cover that.

Linebreaks are not handled well yet.  That's next.
Also, OT for changes which come in while we're writing.
remove explicit save button
Support multi-line documents

Document contents is now an array of strings.  It's rendered by
including a <br> between each string.

This matches reasonably well with the contentEditable behavior in
Firefox.  Safari does some more fancy things with divs.

Reading the modified buffer into an array of strings: we keep text
nodes, and recurse into others.  In addition, we check for repeated <br>
tags (or <br> tags inside divs) and add an empty line so they will be
reconstituted.
logo links to home
Create documents from home

Current flow: there's a title field on home.  Enter text and press
return, and this creates your document and jumps to its view/edit page.
The document is pre-filled with the text "Click here to edit this document".

Future: title field isn't always there, only appears on clicking "New"?