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.

#!/bin/sh

CHEF_DIR=`dirname $0`
if `hash readlink 2>&-`; then
    LINKED_EXE=`readlink $0`
    if [ -n "$LINKED_EXE" ]; then
        CHEF_DIR=`dirname $LINKED_EXE`
    fi
fi
python $CHEF_DIR/../chef.py $@