Begin adding flush option for v4 and v6 pools.
Add flush operation to man page
Change arg letter
Add flush functions to userspace tool
Naive pool flush
Merge branch 'feature/flush' of https://github.com/realloc/NAT64 into issue97

Conflicts:
	include/nat64/comm/config_proto.h
	usr/src/jool.c
	usr/src/pool4.c
	usr/src/pool6.c