Issue #260: Now using Respect\Validation exceptions only

* `ExceptionInterface`: all Respect\Validation\Exceptions implement through inheritance
* `ValidatorExceptionInterface`: implemented only by AllOfException.  This allows the end users to know when there has been a Validator exception rather than just any of our exceptions.

Fixed formatting issues

Created two new exception types

* Created ValidationExceptionInterface
* Created NestedValidationExceptionInterface which extends ValidationExceptionInterface
    * Renamed from ValidatorExceptionInterface

* ValidationException implements ValidationExceptionInterface and ValidationExceptionTest checks for the implementation.
* AbstractNestedException implements NestedValidationExceptionInterface and AbstractNestedExceptionTest checks for the implementation.

* CheckExceptionsTest now checks all Rule exceptions to make sure they implement ValidationExceptionInterface
* ValidatorTest now contains test that shows that only ValidationExceptionInterface can be used reliably with `::check()`

* Updated documentation for new exception types
* Reworked examples to show how to catch the exception interfaces

Minor changes in readme.md and ExceptionInterfaces

* Removed `import` statements (hahaha)
* Renamed `$e` to `$exception`

* `ValidationExceptionInterface` now extends `ExceptionInterface`.  Changed `ValidationException` to match

library/Exceptions/NestedValidationExceptionInterface.php

@@ -0,0 +1,8 @@
+<?php
+namespace Respect\Validation\Exceptions;
+
+interface NestedValidationExceptionInterface extends ValidationExceptionInterface
+{
+    public function findMessages(array $paths);
+    public function getFullMessage();
+}