MINOR: add a simple way to iterate through version numbers in reverse order.
MINOR: modify the log standard output.

The new output use one line per file in the db and, in addition, one line
per version in the db, listed in reverse chronological order.
MINOR: add another ouput format for the log with an associated option.
Merge branch 'log-cmd'
Merge pull request #5 from fabrice-rossi/master

MINOR: New output formats for the log command