Add Markov.add function

This is basically just a shorthand, but also abstracts away adding a
line to a markov chain

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

tools/markov_import.py

@@ -37,5 +37,5 @@ if __name__ == "__main__":
                 if mat := LINE_RE.search(line):
                     name = mat["name"]
                     message = mat["message"]
-                    plugin.chains[channel][name].add(message)
+                    plugin.add(channel, name, message)
     plugin.save()