Initial double blink example.
Double blink example actually blinks on two ports.
Clean up.
Replace AST.Stream with AST.Expression.
Make type safe AST constructors with help of phantom type.
Double blink example inverts second blink.
Clarify name.
Arduino program writers just need to import Arduino module.
Programs are clearer because of monadic stucture.
Language module contains code construct type safe program.
Clean up.
Rename Language moudle to DSL.