Reorganize dartdoc to new package layout.

Reorganize dartdoc to new package layout.

Committed: https://code.google.com/p/dart/source/detail?r=12338

[Bob Nystrom, 2012-09-13 01:55:29]

This patch isn't as scary as it looks. It's mostly just moving files around and
then fixing the import paths as a result of that.

This gets dartdoc to use the new "lib/" package layout described here:
http://www.dartlang.org/docs/pub-package-manager/package-layout.html

By M1, I intend to remove support from pub for the old layout style, so it's
important that everything in pkg is updated. I've got most of the stuff fixed
(or have fixes in flight). See here for more:
http://code.google.com/p/dart/issues/detail?id=5106

I tested this by:
1. Running dartdoc from the repo.
2. Running apidoc from the repo.
3. Building the SDK.
4. Running dartdoc from the SDK.

And it seems to look OK.

[Johnni Winther, 2012-09-13 06:48:59]

lgtm