Enable to specify disks with path to device file
or with symbolic link to the device file.

For example:
dstat -d -D /dev/vda2
dstat -d -D /dev/disk/by-id/scsi-SATA_Hitachi_HDP7250_GEA534RF3YYMMA-part3
dstat -d -D /dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0-part2
dstat -d -D /dev/disk/by-uuid/6df45ed6-c4ad-4054-955d-b15102f2c566
Rename get_disklist() to basename() and move it out of the Options class to respective plugin classes.
Document new --bits option.
Make --help and man page consistent.
Merge pull request #8 from jpopelka/master

[Feature] Enable to specify disks with path (symlink) to device file