First stab at #135 - Add borders (#200)

Fixes #135

Added border support for ODS and XLSX files.
Updated README.

src/Spout/Writer/Style/StyleBuilder.php

@@ -121,6 +121,18 @@ class StyleBuilder
         return $this;
     }
 
+    /**
+     * Set a border
+     *
+     * @param Border $border
+     * @return $this
+     */
+    public function setBorder(Border $border)
+    {
+        $this->style->setBorder($border);
+        return $this;
+    }
+
     /**
      * Returns the configured style. The style is cached and can be reused.
      *