[lib] Split Bridge/Cache/Format into one file per class

The files have grown to a size where it is necessary to search
for a class in a file. This commit splits the content into one
file per class. RSS-Bridge will require implementations and
the implementations will require (once) the interfaces.

lib/CacheAbstract.php

@@ -0,0 +1,11 @@
+<?php
+require_once(__DIR__ . '/CacheInterface.php');
+abstract class CacheAbstract implements CacheInterface{
+    protected $param;
+
+    public function prepare(array $param){
+        $this->param = $param;
+
+        return $this;
+    }
+}