First usable release after some heavy reworks

All issues in #53 have been resolved among many other. bookwyrm is still
considered unstable, or at least in some beta-phase; this release was
somewhat rushed just because I wanted it out the door. Here it is.

Highlights of this release are:
* improved log handling and C++-Python interfacing;
* learned --accuracy option, specifying fuzzy string match accuracy;
* adhered to the modifier passed to --year;
* display how many plugins are still running;
* fix and overhaul plugins/;
* add a test framework with some tests - run these with ctest(1);
* overhauled Python API to only rely on dicts (more Pythonic);
* resolve mirrors only for items that the user wants to download:
    * HTTP headers can be returned and set before download;
* overhauled out-of-code documentation, and
* added a

Future releases will likely refer to this changelog instead of inlining
changes here.