Rename --[no]-dry-run to --[no]-go
Add progress indication during initial scan for music
Add rudimentary configuration file support

The configuration file is stored in ~/.morc, and is in ini format
with three sections: [core], [sort], and [tag].

The options are named after the internal configuration variables,
rather than being parsed as arguments, so (for example) --file-name
and all the --prefix-foo arguments are set using 'file-name=...' in
the config file.

Command line options override options given in the file.

Mine:

[sort]
safe-paths: windows
file-name: {disc?}{track!d:02d} - {title}
Trim description for sort, add one for tag
Add 'mo sort --mode' command line flag
Add 'mo sort --skip-existing' flag
Properly flush output when scanning tags; add 'subtitle' and 'filename' ID3 tags.
Add some error reporting in cases where it can't set the tags.