Re-add logging, rem file filters.

Add:
    bitshift/
        __init__.py
            -add `_configure_logging()`, which sets up a more robust logging
            infrastructure than was previously used: log files are rotated once
            per hour, and have some additional formatting rules.

        (crawler, indexer).py
            -add hierarchically-descending loggers to individual threaded
            classes (`GitHubCrawler`, `GitIndexer`, etc.); add logging calls.

        indexer.py
            -remove file filtering regex matches from `_get_tracked_files()`,
            as non-code files will be discarded by the parsers.