disk: Distinguish between IEC, SI and custom prefixes

* IEC: Ki, Mi, Gi, Ti (powers of 1024)
* SI: k, M, G, T (powers of 1000)
* custom: K, M, G, T (powers of 1024)
update CHANGELOG
manpage: update version number
man: Add a missing colon
Add a format_down example for battery
Add hide_seconds option

fixes: #1134
Merge remote-tracking branch 'upstream/master'