Implement a somewhat Perl-style grep in Go
import "github.com/CharlesGriswold/grep"
func Grep(ss []string, pat string) (ret []string)
func Grepnot(ss []string, pat string) (ret []string)
Grep functions similarly to grep /pat/, @string; in Perl, and Grepnot is similar to grep !/pat/, @string;.
Grep returns the strings that match the pattern and Grepnot returns the strings that do not match the pattern.
An empty string does not match the pattern. The logic on this has to be explicit since Go's regular expressions don't like empty strings.