… default shared API key has been removed.

  Keys are easy to register via https://thetvdb.com/api-information
- Include cache location info in debug logging
- Drop support for Python 2.6 (EOL 2016), 3.3 (EOL 2013), 3.4 (EOL 2019)
- Removed deprecated `Tvdb(debug=...)` argument - use logging module instead.
  E.g `logging.basicConfig(level=logging.DEBUG)`
- Removed long deprecated `tvdb_ui` and `tvdb_exceptions` modules.
  Everything in these are accessible via the `tvdb_api` module
- Correctly errors when failing to find show by ID -
  [issue #54](https://github.com/dbr/tvdb_api/issues/54)
- Web-cache filename contains major version of Python to support
  side-by-side usage of `tvdb_api` in Python 2 and 3
- Fix bug causing occasional `KeyError` when looking up lots of shows.
  [PR #65](https://github.com/dbr/tvdb_api/pull/65)