Add support for styling

Added top level methods on the Writer:
 - addRowWithStyle()
 - addRowsWithStyle()

Added a style builder, to easily create new styles.
Each writer can specify its own default style and all styles will automatically inherit from it.

For now, the style properties supported are:
 - bold
 - italic
 - underline
 - strikethrough
 - font size
 - font name
 - wrap text (alignment)

src/Spout/Writer/WriterInterface.php

@@ -40,6 +40,19 @@ interface WriterInterface
      */
     public function addRow(array $dataRow);
 
+    /**
+     * Write given data to the output and apply the given style.
+     * @see addRow
+     *
+     * @param array $dataRow Array of array containing data to be streamed.
+     * @param Style\Style $style Style to be applied to the row.
+     * @return WriterInterface
+     * @throws \Box\Spout\Common\Exception\InvalidArgumentException If the input param is not valid
+     * @throws \Box\Spout\Writer\Exception\WriterNotOpenedException If this function is called before opening the writer
+     * @throws \Box\Spout\Common\Exception\IOException If unable to write data
+     */
+    public function addRowWithStyle(array $dataRow, $style);
+
     /**
      * Write given data to the output. New data will be appended to end of stream.
      *
@@ -55,6 +68,19 @@ interface WriterInterface
      */
     public function addRows(array $dataRows);
 
+    /**
+     * Write given data to the output and apply the given style.
+     * @see addRows
+     *
+     * @param array $dataRows Array of array containing data to be streamed.
+     * @param Style\Style $style Style to be applied to the rows.
+     * @return WriterInterface
+     * @throws \Box\Spout\Common\Exception\InvalidArgumentException If the input param is not valid
+     * @throws \Box\Spout\Writer\Exception\WriterNotOpenedException If this function is called before opening the writer
+     * @throws \Box\Spout\Common\Exception\IOException If unable to write data
+     */
+    public function addRowsWithStyle(array $dataRows, $style);
+
     /**
      * Closes the writer. This will close the streamer as well, preventing new data
      * to be written to the file.