zramctl: add details to --size option documentation

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

Signed-off-by: Karel Zak <kzak@redhat.com>
zramctl: improve error message

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
zramctl: cannonicalize devname when no fullpath specified

Signed-off-by: Karel Zak <kzak@redhat.com>
zramctl: add bash completion script

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

Use of --algorithm or --streams is not expected to work without
reseting device, that happens when --size is specified, so ensure the
former options to be combined with the later.

[kzak@redhat.com: - make it more generic]

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
Signed-off-by: Karel Zak <kzak@redhat.com>