Fix the documentation. Check terminology consistency before release

[m0rjc]

The documentation needs to be checked.

Document the methods in custom stores.

Document the new internal packages in doc.go

Check terminology.

• Is it a readpipeline or a pipeline , process or pipe?
• What does the Pipe() method do?
• FieldProcessor[T], Pipeline[T],....?

My IDE auto-filled the type name for FieldProcessor[T] from the internal package when writing a goconfig.Validator[T]. Try to make the type aliases fix this, without breaking Go's type system.