tabular output for metadata

[acrisci]

The current output format for the metadata command gives the GVariant format which is not very readable.

Change $ playerctl metadata tsv output which is human readable and fairly machine readable. It gets a little tricky with lists though. Probably just output a comma separated list in that case.

xesam:title      Rise
xesam:artist     Katy Perry
xesam:album      Rise
...

[acrisci]

Changing this to tabular output since tsv doesn't look good on the command line.