Add output filename example to audiotools-config interactive mode.

Bump version to 2.20 alpha 1.
Update minimum Python version to 2.7.0

This offers a lot of stuff standard that will be useful going forward.
Convert track2track to use argparse module for arguments.
Convert most utilities to argparse instead of optparse.
Convert remaining utilities to argparse
Update ProgressDisplay interface.

This frees the user from having to manage row_ids manually.
Fix temporary file management, mostly for setting metadata.

This creates a new temporary file alongside the original
which is then renamed over the original at close()-time.
It has the advantages of not only preserving the original file's permissions
(which I hadn't been doing before), but also behaves better
when a disk fills up since the original doesn't get changed until
commit-time.
Cleanup Unicode output formatting primatives.

Shift the ANSI escape formatting to the output_text class
and move all the table handling to its own class, independent of
the Messenger classes.

This allows a lot of metadata raw output to use the same table formatting
as everything else, which is useful.
Update documentation for new text interface.
Switch table divider character to Unicode one.
Add --version check to utilitys' unit tests.
Replace Messenger function with Messenger object.

This removes the Verbose/SilentMessenger split
and makes the design a little simpler.
Fix AccurateRip calculation routine.

Ensure it accounts for first and last tracks properly.
Add AccurateRip v2 checksum support.

Nothing to attach it to yet, but it's one less thing to worry about later.
Update trackverify's AccurateRip output summary.

It now displays the calculated checksum in a table
which is more useful for debugging and cross-referencing purposes.
Fix track2cd to always account for write offset, if any.
Ensure unwriteable files aren't overwritten by set/update_metadata

TemporaryFile's method of write/rename doesn't account for
an unwriteable file, so it's best to test for writeability
beforehand.