importing sam leffler's libstatfoo into -HEAd

hi,

i'd like to import the libstatfoo code from sam into -HEAD.

It's used by some of the wifi tools to print out periodic and global
statistics. It abstracts away the gathering, printing and formatting
bits.

I'm hoping that we can adapt some of the other base tools to use it
and then teach it to print out statistics in other (machine parsable)
formats, so we don't have to keep hacking at the tools to do this.

The initial import:

http://people.freebsd.org/~adrian/patches/20140304-libbsdstatfoo.diff

Thanks!


-a