Make Blueprint class extensible

[jasonmccreary]

While the Blueprint class has methods to register additional lexers and generators it is created within the command and as such not readily extensible.

Potential options:

• resolved as a singleton to share the same object with other components
• allow publishing of a configuration file to register additional functionality

[ttomdewit]

You could consider https://laravel.com/docs/6.x/providers#deferred-providers and see if you can "tag" generator packages as such. I think from within the main Blueprint package you can find all tagged services (https://laravel.com/docs/5.8/container#tagging).

Make sure these adhere to a common contract so the main package doesn't really know what generators are available, it just knows how to use them.