Allow blocking "say" feature with a new plugin

Let's say this resolves zigdon#90, and if "say" is eventually removed from core
and put into a plugin then that can replace this one.

plugins/plugin.nosay.pl

@@ -0,0 +1,30 @@
+# BUCKET PLUGIN
+
+use BucketBase qw/cached_reply Log/;
+
+sub signals {
+    return (qw/on_public/)
+}
+
+sub route {
+    my ( $package, $sig, $data ) = @_;
+
+    if ( $sig eq 'on_public' ) {
+        # first check if the line looks like teaching a factoid
+        if ( $data->{msg} =~ /(.*?) (?:is ?|are ?)(<\w+>)\s*(.*)()/i
+             or $data->{msg} =~ /(.*?)\s+(<\w+(?:'t)?>)\s*(.*)()/i
+             or $data->{msg} =~ /(.*?)(<'s>)\s+(.*)()/i
+             or $data->{msg} =~ /(.*?)\s+(is(?: also)?|are)\s+(.*)/i ) {
+            return 0;  # if it looks like teaching, let processing continue
+        # then if not, check if it would trigger the 'say' function
+        } elsif ( $data->{msg} =~ /^say (.*)/i ) {
+            if ( $data->{addressed} ) {
+                &cached_reply( $data->{chl}, $data->{who}, "", "don't know" );
+            }
+            Log "$data->{who} tried to trigger 'say' in $data->{chl}; ignoring.";
+            return 1;  # Halting core prevents default behavior, but plugins should (probably?) be allowed to continue
+        }
+    }
+
+    return 0;
+}