Use hack-codegen v2.1, use shapes for URIBuilders and request parameters

Documentation is still the blocker on moving out of RC state.

Hack-Codegen

facebook/hack-codegen v2.1 or above is now required; the 2.x series is a major break from 1.x; please see:

• release notes for v2.0
• release notes for v2.1

Shapes for URIBuilders

Old:

$uri = (new FooControllerUriBuilder())->setHerp('herp')->setDerp('derp')->getPath();
// or, if using trait:
$uri = FooController::getUriBuilder()->setHerp('herp')->setDerp('derp')->getPath();

New:

$uri = FooControllerUriBuilder::getPath(shape('herp' => 'herp', 'derp' => 'derp'));
// or, if using trait:
$uri = FooController::getPath(shape('herp' => 'herp', 'derp' => 'derp'));

The primary benefit is that instead of depending on runtime enforcement, the typechecker will now tell you if you are missing a required parameter.

Shapes for request parameters

Old:

$foo = $this->getParameters()->getFoo();

New:

$foo = $this->getParameters()['foo'];

The benefits are:

• consistency with URI builders
• able to easily get a link to the current page by passing the request parameters shape directly to the URI builder
• If you use the trait, you only need to specify how to get the underlying non-codegen parameters object, not provide the full method implementation.

Misc

• added <<Codegen>> attribute to generated classes and tests
• added discardChanges bool option to configuration shape; this will ignore signatures, and remove any changes outside of manual sections.