Refactor readers for better di (#457)

* Refactor readers to get a proper DI

Similar to what was done with writers, readers also needed to be updated to match the new way of doing things.
This commits promotes a better DI (factories, injection through constructors).

* Escapers should not be singletons

Instead, they should be proper object that can be injected where needed.

src/Spout/Common/Helper/Escaper/EscaperInterface.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Box\Spout\Common\Helper\Escaper;
+
+/**
+ * Interface EscaperInterface
+ *
+ * @package Box\Spout\Common\Helper\Escaper
+ */
+interface EscaperInterface
+{
+    /**
+     * Escapes the given string to make it compatible with PHP
+     *
+     * @param string $string The string to escape
+     * @return string The escaped string
+     */
+    public function escape($string);
+
+    /**
+     * Unescapes the given string to make it compatible with PHP
+     *
+     * @param string $string The string to unescape
+     * @return string The unescaped string
+     */
+    public function unescape($string);
+}