Additional improvements/fixes

Hi,

Here's another set of patches. This concludes the major changes that I wanted to make, so subsequent patches should be much smaller and address only an issue or two at a time.

Summary of changes in this pull request:

- Improved tag scrubbing (mostly for numeric tag types).
- Output release URL for better logging/easier investigation of problem torrents.
- Inform the user when an original release has bad required tags (trump candidate).
- Remove support for downmixes. The rules for when they're allowed are complicated, best to be safe.
- Use What.CD wiki-recommended dithering process. Should result in improved 24->16 transcodes.
- Use recommended -h flag with 320 CBR transcodes.
- In upload description, include a permalink to the original release, an example of the transcode process command line (fixes #40), and the version of whatbetter used for the transcode.
- Bump the version number to 1.1.

Thanks again for this great script!