Add option to allow filter by exact prefix (not including sub prefixes)

[digizeph]

For example, the following command outputs updates for the desired subprefixes as well.
bgpreader -k 195.0.0.0/8 -w 1572371400,1572372000 -t updates

...
U|A|1572371860.000000|routeviews|route-views2|||3277|195.208.112.161|195.88.254.0/23|195.208.112.161|3277 3267 1299 6762 8932 44395 210315|210315|3277:39710||
U|A|1572371860.000000|routeviews|route-views2|||3277|195.208.112.161|195.133.223.0/24|195.208.112.161|3277 3267 8932 8932 8932 8932 208293 57324 203217 203217|203217|3277:39710||
U|A|1572371860.000000|routeviews|route-views2|||3277|195.208.112.161|195.69.228.0/24|195.208.112.161|3277 3267 8932 8932 8932 39216 39216 39216 202316|202316|3277:39710||
U|A|1572371860.196486|routeviews|route-views.amsix|||267613|80.249.213.223|195.74.94.0/24|80.249.213.223|267613 42652|42652|5469:2400 5469:10001 5469:11002||
U|A|1572371860.196486|routeviews|route-views.amsix|||267613|80.249.213.223|195.242.162.0/24|80.249.213.223|267613 42652|42652|5469:2400 5469:10001 5469:11002||
...

Not sure if this is the desired behavior by design.