[BUGFIX] Tune GranuarityInterface

GranuarityInterface is the main interface of
granularities. It should extend both \ArrayAccess
and \Countable directly and shouln't define
ArrayAccess methods like offsetExists() again.

This kinda fixes cogpowered#2
even though the PHP 5.3 problem is not an issue here anymore.

src/cogpowered/FineDiff/Granularity/Granularity.php

@@ -21,7 +21,7 @@
 /**
  * Granularities should extend this class.
  */
-abstract class Granularity implements GranularityInterface, \ArrayAccess, \Countable
+abstract class Granularity implements GranularityInterface
 {
     /**
      * @var array Extending granularities should override this.

src/cogpowered/FineDiff/Granularity/GranularityInterface.php

@@ -18,13 +18,8 @@
 
 namespace cogpowered\FineDiff\Granularity;
 
-interface GranularityInterface
+interface GranularityInterface extends \ArrayAccess, \Countable
 {
-    public function offsetExists($offset);
-    public function offsetGet($offset);
-    public function offsetSet($offset, $value);
-    public function offsetUnset($offset);
-
     /**
      * Get the delimiters that make up the granularity.
      *