Fixed issue #22 related to compatibility on Python3.6 interpreters.

Fixed an accidental revert of PR #14

Adds a hotfix for a bug with directory paths in storage.config

Features fixes for crashes in certain scenarios, contributed by @limited

This patches a common case for large stripes where the offset to a copy B metadata will be miscalculated and cause a crash. It now falls back on copy A when that happens, but that means the metadata is possibly out-of-date.

This release fixes long-standing issues with multi-volume spans. It also addresses a bug where an old version of a directory would be read in rather than the current one. Finally, this release also targets a bug related to batch processing of a span's stored objects that was previously unknown (because those other two bugs invariable caused crashes under conditions that exposed this one) and dumping a span that has fewer stored objects than the system has CPUs will now fall back on a single-threaded approach.

Features some fixes for virtual testing environments, and a fix for relative-path cache definitions.

Bugfix: scan now handles multiple stripe definitions better than previously (which was not at all).
Also added a bit more debugging information related to span and stripe construction

This version fixes a bug with reading disk headers on spans containing more than one stripe, as well as a bug with menu option 6 that was causing it to crash because I don't know how to hit ^F. Or ^R. Or ^B, or really just even look at my own code.

This release introduces the new command line flag -D/--dump-breakdown which works much like the -d/--dump flag except that it will dump stats on a per-hostname basis as opposed to dumping stats for every unique URL in the cache. Output is in TYAML format.

This release also changes the call signature of a couple functions in the ui and config modules and causes config.spans() to output the cache spans in sorted order of filename, which goes partway toward resolving #9 .