this allows implementing __call() in behaviors

See this forum topic for details:
http://www.yiiframework.com/forum/index.php/topic/46629-invoke-behavior-method-through-php-magic-method-call-dosent-work/

return false, not null

- cleanup API and usage, add documetation link
- introduced @property feature in getter or setter which has precedence
  over @return or @param tag if present

helps reducing weird error messages.