Add Flux from() and filter() methods

Signed-off-by: davidarendsen <davidarendsen@hey.com>

src/Function/Base.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace Arendsen\FluxQueryBuilder\Function;
+
+abstract class Base {
+
+	/**
+	 * @throws FunctionNotImplementedException
+	 */
+	public function __toString()
+    {
+		throw new FunctionNotImplementedException('__toString', get_class($this));
+	}
+
+}