provide create_diskmap() function
BUGFIX fail if trying to configure same device twice
add a visual separator
update LVM documentation
add verify() function

This function is intended to find logical errors, like
 - using a non existing device
 - using the same disk by different name (e.g. 'sda' and 'disk1')
 - using the same mountpoint multiple times
 [...]
use a common directory to provide parser input