sources: Make the `SimplePageSource` more extensible, fix bugs in `prose` source. The `SimplePageSource` now calls a `_populateMetadata` function that subclasses can override to add/edit their custom metadata everwhere it would be returned to the system.

#!/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 $@