Separate annotations from builders

[thosakwe]

Having both the annotations and the build_runner and source_gen dependencies renders this package unusable in many situations.

I was trying to install the gitter library as a dependency in a project, and it depends on jaguar_serializer. However, I have other builds in my project, which require source_gen >= 0.6.0. As you can imagine, pub get fails.

The most common solution to this is to split into two packages, for example:

• built_value and built_value_generator
• angel_orm and angel_orm_generator

[lejard-h]

plan for 0.4.0, note that gitter package is now working without jaguar_serializer