Moved readers to iterators

Instead of the hasNext() / next() syntax, readers now implements the PHP iterator pattern.
It allows readers to be used with a foreach() loop.

All readers now share the same structure (CSV is treated as having exactly one sheet):
- one concrete Reader
- one SheetIterator, exposed by the Reader
- one or more Sheets, returned at every iteration
- one RowIterator, exposed by the Sheet

Introducing the concept of sheets for CSV may be kind of confusing but it makes Spout way more consistent.
Also, this confusion may be resolved by creating a wrapper around the readers if needed.

-- This commit does not delete the old files, not change the folder structure for Writers. This will be done in another commit.

src/Spout/Reader/CSV/Reader.php

@@ -0,0 +1,95 @@
+<?php
+
+namespace Box\Spout\Reader\CSV;
+
+use Box\Spout\Reader\AbstractReader2;
+use Box\Spout\Common\Exception\IOException;
+
+/**
+ * Class Reader
+ * This class provides support to read data from a CSV file.
+ *
+ * @package Box\Spout\Reader\CSV
+ */
+class Reader extends AbstractReader2
+{
+    /** @var resource Pointer to the file to be written */
+    protected $filePointer;
+
+    /** @var SheetIterator To iterator over the CSV unique "sheet" */
+    protected $sheetIterator;
+
+    /** @var string Defines the character used to delimit fields (one character only) */
+    protected $fieldDelimiter = ',';
+
+    /** @var string Defines the character used to enclose fields (one character only) */
+    protected $fieldEnclosure = '"';
+
+    /**
+     * Sets the field delimiter for the CSV.
+     * Needs to be called before opening the reader.
+     *
+     * @param string $fieldDelimiter Character that delimits fields
+     * @return Reader
+     */
+    public function setFieldDelimiter($fieldDelimiter)
+    {
+        $this->fieldDelimiter = $fieldDelimiter;
+        return $this;
+    }
+
+    /**
+     * Sets the field enclosure for the CSV.
+     * Needs to be called before opening the reader.
+     *
+     * @param string $fieldEnclosure Character that enclose fields
+     * @return Reader
+     */
+    public function setFieldEnclosure($fieldEnclosure)
+    {
+        $this->fieldEnclosure = $fieldEnclosure;
+        return $this;
+    }
+
+    /**
+     * Opens the file at the given path to make it ready to be read.
+     * The file must be UTF-8 encoded.
+     * @TODO add encoding detection/conversion
+     *
+     * @param  string $filePath Path of the CSV file to be read
+     * @return void
+     * @throws \Box\Spout\Common\Exception\IOException
+     */
+    protected function openReader($filePath)
+    {
+        $this->filePointer = $this->globalFunctionsHelper->fopen($filePath, 'r');
+        if (!$this->filePointer) {
+            throw new IOException('Could not open file ' . $filePath . ' for reading.');
+        }
+
+        $this->sheetIterator = new SheetIterator($this->filePointer, $this->fieldDelimiter, $this->fieldEnclosure, $this->globalFunctionsHelper);
+    }
+
+    /**
+     * Returns an iterator to iterate over sheets.
+     *
+     * @return SheetIterator To iterate over sheets
+     */
+    public function getSheetIterator()
+    {
+        return $this->sheetIterator;
+    }
+
+
+    /**
+     * Closes the reader. To be used after reading the file.
+     *
+     * @return void
+     */
+    protected function closeReader()
+    {
+        if ($this->filePointer) {
+            $this->globalFunctionsHelper->fclose($this->filePointer);
+        }
+    }
+}