Improve callmap with information from docs.php.net (#494)

* Update CallMap.php with information from docs.php.net

* Undo possibly inaccurate information from docs.php.net

* Fix bug in ReflectionMethod::invoke*() signature

http://php.net/manual/en/reflectionmethod.invoke.php had a misleading
method signature description section

tests/ArgTest.php

@@ -15,7 +15,7 @@ class ArgTest extends TestCase
             'callMapClassOptionalArg' => [
                 '<?php
                     $m = new ReflectionMethod("hello", "goodbye");
-                    $m->invoke("cool");',
+                    $m->invoke(null, "cool");',
             ],
             'sortFunctions' => [
                 '<?php