docs: add details to zramctl --size option documentation

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
zramctl: mark --reset mutually exclusive with --algorithm and --streams

Reset is setting algorithm to lz4 and streams to 1.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
zramctl: fail status printout when device does not exist

Earlier.

$ zramctl zram313 ; echo $?
0

Now.

$ zramctl zram313 ; echo $?
zramctl: zram313: no such device
1

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
zramctl: improve error message

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
zramctl: fix mount point printout

This change adds full path to the device name when status is requested
using a short device name, such as zram3.  See sample below how a device
mount point was printed earlier without and with full device path.

$ zramctl zram3
NAME  ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT
zram3 lz4             1M   4K   62B    4K       1

$ zramctl /dev/zram3
NAME       ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram3 lz4             1M   4K   62B    4K       1 [SWAP]

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
zramctl: add bash completion script

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
zramctl: allow use of --algorithm and --streams alone

Earlier the --algorithm and --streams had to be combined with --size.  To
user requirement to combine with --size was indirectly told using
following message.

$ zramctl --stream 3 zram3
zramctl: options --algorithm, --find and --streams are mutually exclusive

Signed-off-by: Sami Kerola <kerolasa@iki.fi>