Use PHP attributes to define templates

Creating a specific exception for each rule adds a painful overhead. If
you want to make a custom message for your rule, you will need to create
an exception and then register that exception namespace to be able to
use it—all that is just for customizing the message of your rule.

Having different namespaces also implies that you need to fetch the
exception of the rule from another directory to change it. As Uncle Bob
said, "Classes that change together belong together. Classes that are
not reused together should not be grouped."

This commit will drastically change this library, moving all the
templates from the exceptions to the rules. Consequently, the Factory
becomes much simpler, and the library gets a bit smaller, too.

Signed-off-by: Henrique Moody <henriquemoody@gmail.com>

library/Exceptions/NestedValidationException.php

@@ -231,6 +231,6 @@ class NestedValidationException extends ValidationException implements IteratorA
             return $childException->hasCustomTemplate();
         }
 
-        return !$childException instanceof NonOmissibleException;
+        return !$childException instanceof NonOmissibleValidationException;
     }
 }