This affects the cache_dir and the as-yet-unused state_dir. It uses
the shellexpand and directories crates so that the default values
can be constant strings that use variables to refer to the right
default locations.
This commit adds configuration options for these values, with the
right defaults, and uses those options instead of built-in functions
to set them.
We also remove the function to extract information from chutney
directories: now that arti is configurable, it can be chutney's job
to make its own network configurations.
Nick Mathewson
George Kadianakis