Switch to treating parsed values from /proc/meminfo as kibibytes. Previously, it was treated as kilobytes, but apparently that's not correct, as per this Red Hat doc:

While the file shows kilobytes (kB; 1 kB equals 1000 B), it is actually kibibytes (KiB; 1 KiB equals 1024 B). This imprecision in /proc/meminfo is known, but is not corrected due to legacy concerns - programs rely on /proc/meminfo to specify size with the "kB" string.

Fixes: #341