Consider adding .rei files and hiding unsafe constructors for all data types

[andywhite37]

In relude-parse, @mlms13 added .rei files for the "extra" parser types that we have, so that we can have more safety and explicitness around how one can construct values of a certain type.

The .rei files make the types abstract, hide the data constructors, and only allow construction of values through parse functions, or through unsafeMake escape hatches, which throw exceptions for invalid input.