caching: Use separate caches for config variants and other contexts. * The `_cache` directory is now organized in multiple "sub-caches" for different contexts. * A new context is created when config variants or overrides are applied. * `serve` context uses a different context that the other commends, to prevent the `bake` command's output from messing up the preview server (e.g. with how asset URLs are generated differently between the two). * Fix a few places where the cache directory was referenced directly.

from textile import textile
from piecrust.formatting.base import Formatter


class TextileFormatter(Formatter):
    FORMAT_NAMES = ['textile', 'text']
    OUTPUT_FORMAT = 'html'

    def render(self, format_name, text):
        assert format_name in self.FORMAT_NAMES
        return textile(text)