move parse_option_size to lib/option.c

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
sheep: make option set human friendly

With this patch, journal size and object cache size should be set with human
friendly value like 200G, 2000M.

This patch breaks compatibility of command line.

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>