Consider moving feeders to separate packages

[stephenafamo]

Having each feeder it their own package means that using one feeder does not add all the other dependencies to a project.

Currently, using any feeder will cause the env, dotenv, yaml, and toml modules to be included as dependencies.
As the number of feeders increases this will also add more and more dependencies.

If they are in separate packages, while all the dependencies will show up in this module's go.mod, a dependent package will only get the dependencies for the feeder they use.

[miladrahimi]

It sounds like a good idea. I'll consider it in the next version.