[new] textproc/grepcidr3 3.0

Hi all,

Attached is a port of textproc/grepcidr3, this fork of grepcidr has a
few command line options that the original lacks, such as -D:

$ echo 10.1.1.0/24 | grepcidr3 -D 10.1.1.1
10.1.1.0/24

I added 2 patches:
* rename the utility to 'grepcidr3' (in order to avoid naming collisions)
* add pledge("stdio rpath", NULL) in main().

OK?

Kind regards,

Job