improved metadata handling

Move parsing of metadata into declare-time. This should speed the
command building loop greatly on longer albums or when given lots of
metadata... and especially both.

When building the command, if both the track-specific metadata and
non-track-specific metadata are not declared, skip over them.

When track specific metadata is given, it will always override
non-track-specific metadata.

If track-specific metadata is given for artist or album, these are not
used to compute save path.
remove dry run message

It should be pretty obvious when you dry run versus actually execute
ffmpeg commands.
* version 1.2