Improvements to commands 'music list' and 'align'

The 'align' command now receives arguments as options, and is also
capable of aligning columns to the left and to the right.

The 'music list' command now takes advantage of the improved 'align'
command to align some columns to the right, namely the columns showing
numeric values.
Complete rewrite of the music command

Now this command has better support for parsing and handling diverse
command line options, and individual help messages for each of the
subcommands it supports.