Instance rules are not shared among other validator
objects (thus they are not static). This is useful
if you have a rule you do not want your other validators
to use (because it is very special to this validator).
The parameter given to addInstanceRule is identically to
addRule:
public function addInstanceRule(string $name, callable $callback [, string message])
Instead of appending to the static variables $_rules, and
$_ruleMessages, it now appends to $_instanceRules and
$_instanceRuleMessages.
A new getter for the rules and ruleMessage has also been added:
public array getRules()
public array getRuleMessages()
All existing code has been updated to use getRules(), and
getRuleMessages() instead of $_rules, and $_ruleMessages.
