VOLUME: all operations take sizes in bytes

The implementations are free to round up to a convenient block size,
this implementation rounds up to a physical extent.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Allocator: rename 'to_string1' to 'string_of_area'

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
mlvm: parse sizes using suffixes, KiB, MiB, GiB etc

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge branch 'lots-of-fixes' of github.com:djs55/mlvm into lots-of-fixes