ss: Implement automatic column width calculation

ss: Implement automatic column width calculation

Group fitting fields into lines and space them equally using the
remaining screen width for each line. If columns don't fit on
one line, break them into the least possible amount of lines and
keep them aligned across lines.

This is done by:
 - recording the length of the longest item in each column during
   formatting and buffering (which was added in the previous patch)
 - fitting as many fields as possible on each line of output
 - distributing the remaining padding space equally between the
   columns

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>