Use the NamedPropertyHandler feature of v8 to wrap accesses to PHP properties
and methods from JavaScript. This enables us to support property
set/delete/query.
The `in` and `delete` operators in JavaScript work like the `isset()` and
`unset()` functions in PHP. In particular, a PHP property with a null
value will not be `in` the JavaScript object. (This holds when enumerating
all properties of an object as well.)
Because JavaScript has a single namespace for both properties and methods,
we allow the use of the `__call` method on a PHP object (even if the
PHP class does not natively define the `__call` magic function) in order
to unambiguously invoke a method. Similarly, you can prefix a property
name with `$` to unambiguously access the property. (When enumerating all
properties, properties are `$`-prefixed in order to ensure they are not
conflated with method names.)
Use the v8::Signature parameter to FunctionTemplate::New to guarantee that
the info->Holder() is of the proper type when `php_v8js_php_callback` is
invoked.
Add test case demonstrating the segfault (which is now prevented).
