plugins/text_trigger: support '@*' prefix to strip addressee from response

Example:

    <jast> someuser: I'm talking to you about !trigger@* but don't want you
           to get pinged twice...
    <gitinfo> This is the text recorded for '!trigger'.

Signed-off-by: Jan Krüger <jk@jk.gs>
plugins/join: #10: fix command line parsing and interpretation of config

* Idiotically, Perl returns the size of the list if split() is used in scalar
  context. Make sure to use it in list context.
* Port the code that reads the list of channels from the config to the
  new(ish) scheme that uses a hashref instead of an arrayref.

Signed-off-by: Jan Krüger <jk@jk.gs>