This type represents a list of fields someone might want to have
returned.
This can be used together with the query library to build select
statements that return the exact data the user might need or want.
This way we may be able to avoid selecting data one might not need at
the end and therefore provide better performance.
This package will contain all the parameter types that need parsing from
the outside world into internal types.
Each type is required to implement its own UnmarshalJSON. At this point
it should also make the checks, if the incoming data is valid input, but
is not required to check against the database.
Gibheer