Initial setup for file serve

[jaapio]

With this change we provide an internal webserver in the application. And introduce a watch on changes. This introduces a new way of working with guides, allowing users to edit documentation without caring about rerendering.

Optimizations are possible like parsing and rendering a single file to make rerendering faster.

To test this you can run the following steps:

cd app
docker build -t phpdocumentor/guides:local .
cd -
docker run --rm -it -v $(pwd):/project -w /project -p 1337:1337 phpdocumentor/guides:local php -dmemory_limit=4G /project/vendor/bin/guides serve --output=./output docs

We need to build a local docker image because we need some extra php extension to watch file changes.

[garvinhicking]

When editing a file on my macOS (Orbstack) I only get this:

string(24) "Unhandled event mask: 10"

and the file is not re-rendered.

[garvinhicking]

On macOS with the recent change and some deprecation messages in the Ratchet lib / interface, the files do get re-rendered. Looking forward for more :)