Improvements and fixes to incremental baking. * Better handling of the render pass during page rendering. * Used sources are paired with the pass they were used in. * Proper use and invalidation of the rendered segments cache based on render passes. * The `Assetor` is also better tracking what was used in a page. * Add flags on a page to get better caching information for the debug window. * Property invalidation of the previous bake record when needed. * Better information about why pages are delayed.

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()