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.

class TemplateNotFoundError(Exception):
    pass


class TemplateEngine(object):
    EXTENSIONS = []

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

    def renderString(self, txt, data, filename=None, line_offset=0):
        raise NotImplementedError()

    def renderFile(self, paths, data):
        raise NotImplementedError()