Add support for some more highlighting options (nick blacklist, pattern blacklist and "whitelist")

I've added three new highlight-control options to my version of irssinotifier.pl; these are:
* `irssinotifier_ignored_nicks` - a list of nicks to block highlights from (if set). Useful for ignoring highlights from bots.
* `irssinotifier_ignored_highlight_patterns` - a list of regular expressions; if set, if the message matches any of these, then the highlight will not be sent. Useful for ignoring automated messages that you don't care about.
* `irssinotifier_required_highlight_patterns` - a list of regular expressions; if set, the message must match at least one of these in order for a highlight to be sent. Useful for if you have a lot of highlights in irssi but don't want to be notified for most of them.

(I've also got rid of a few stray tabs and replaced them with spaces.)

-Dave