bake: Commonize worker pool code between html and asset baking. The `workerpool` package now defines a generic-ish worker pool. It's similar to the Python framework pool but with a simpler use-case (only one way to queue jobs) and support for workers to send a final "report" to the master process, which we use to get timing information here. The rest of the changes basically remove a whole bunch of duplicated code that's not needed anymore.

colorama==0.3.3
compressinja==0.0.2
Jinja2==2.7.3
Markdown==2.6.2
MarkupSafe==0.23
Pygments==2.0.2
pystache==0.5.4
python-dateutil==2.4.2
PyYAML==3.11
repoze.lru==0.6
smartypants==1.8.6
strict-rfc3339==0.5
textile==2.2.2
Werkzeug==0.10.4