Move exceptions to the main namespace

This is so that we are consistent with other PSRs.

https://groups.google.com/forum/#!topic/php-fig/L8rDUwRFsOU

Author: mnapoli

src/Exception/ContainerException.php renamed to src/ContainerException.php

@@ -3,7 +3,7 @@
  * @license http://www.opensource.org/licenses/mit-license.php MIT (see the LICENSE file)
  */
 
-namespace Psr\Container\Exception;
+namespace Psr\Container;
 
 /**
  * Base interface representing a generic exception in a container.

src/ContainerInterface.php

@@ -5,9 +5,6 @@
 
 namespace Psr\Container;
 
-use Psr\Container\Exception\ContainerException;
-use Psr\Container\Exception\NotFoundException;
-
 /**
  * Describes the interface of a container that exposes methods to read its entries.
  */

src/Exception/NotFoundException.php renamed to src/NotFoundException.php

@@ -3,7 +3,7 @@
  * @license http://www.opensource.org/licenses/mit-license.php MIT (see the LICENSE file)
  */
 
-namespace Psr\Container\Exception;
+namespace Psr\Container;
 
 /**
  * No entry was found in the container.