internal: Get rid of the whole "sub cache" business. * Compute cache keys up front, so the cache directory is only chosen once. * Buffer up config variants to apply before loading the config. Makes it possible to cache variant-resulting configs, too. * Make a factory class to reuse the logic that creates the `PieCrust` object correctly for multi-process workers and such. * Add a test.

# humanstxt.org/
# The humans responsible & technology colophon

# AUTHORS

Ludovic Chabant -- @ludovicchabant

# TECHNOLOGY

PieCrust -- http://bolt80.com/piecrust

# THANKS