Generic LogCategory::log($level, $args)

[thekid]

This pull request adds a generic log() method to util.log.LogCategory which accepts the log level and an array of arguments. This method is the same as the previos protected callAppenders() method, only now public and with a more generic name, so no additional overhead is added.

With this in place, we can easily log events given a level and arguments instead of having to resort to call_user_func. An example where this would be useful can be seen in xp-forge/mustache#1:

{{log info "Look at me!"}}

$engine= create(new MustacheEngine())->withHelpers(array(
  'log' => function($in, $context, $options) use($cat) {
    $cat->log(LogLevel::named($options[0]), array_slice($options, 1));
    return '';  // Remove
  }
);