feat: batch mode

[penryu]

Bare minimum that addresses the behavior requested. Does not attempt to refactor main() (which may be warranted).

Keeps the field order, precision, and filtering from the primary functionality (via App).

Addresses #42

[penryu]

Sample output (piped to cat to ensure stdout != tty):

FreeBSD

$ ztop -cd2 | cat
ops_r	r_s	ops_w	w_s	ops_d	d_s	name
7	72	2	27	0	0	zroot
5	25	0	2	0	0	zroot/ROOT
2	45	1	13	0	0	zroot/home
0	2	1	12	0	0	zroot/tmp
0	0	0	0	0	0	zroot/usr
0	0	0	0	0	0	zroot/var

Ubuntu Linux

$ ztop -f '(bunker|USERDATA)' | cat
ops_r	r_s	ops_w	w_s	ops_d	d_s	name
0	0	0	0	0	0	bunker
12	123	5	36	1	0	bunker/penryu
18	67	12	93	0	0	bunker/penryu/work
0	0	0	0	0	0	rpool/USERDATA/home_9ct0pz
0	0	0	0	0	0	rpool/USERDATA/root_9ct0pz