Add new "lafs" program

Add new "lafs" program

"lafs" is similar to "debugfs" for ext[234].

It allows a LaFS to be examined and modified.
Various commands can be enterred, or read from a file.

This preliminary check-in only provides the infrastructure
for reading and parsing commands together with support for
context sensitive completion and help using readline.

Commands implemented are:
  ?  help  exit quit

Naturally more will follow.

Signed-off-by: NeilBrown <neilb@suse.de>