find: Fix the `find` command, add more options. The `--endpoint` option doesn't make any sense anymore since page sources could have non-file-system endpoints. This was replaced with `--name` to match source names instead. Also added `--include-theme`, with filtering out theme pages by default, and `--exact` to explicitely match the given pattern, with matching anything that contains the pattern by default.

PRIORITY_FIRST = -1
PRIORITY_NORMAL = 0
PRIORITY_LAST = 1


class Formatter(object):
    FORMAT_NAMES = None
    OUTPUT_FORMAT = None

    def __init__(self):
        self.priority = PRIORITY_NORMAL

    def initialize(self, app):
        self.app = app

    def render(self, format_name, txt):
        raise NotImplementedError()