Generate elm requests, with types, and JSON encoders, and decoders derived by elm-street, given a servant API.
Header values are passed to the generated request functions as elm Strings.
It is not always clear how to encode custom types automatically so we leave this to the user.
For example, elm-street does not generate string encoders when value constructors take parameters.
We assume that Maybe values will not be used as header types in the targetted API.
The Maybe a type would be suitable for header values when we need to see if the value was parsed correctly and handle the error on our own.
There is a Lenient option for this case though.