Customizable types in sqerl_gobots type specs

[seth]

In the current implementation, we create type specs for the generated functions using a type alias for the record. Some consumers may wish to keep the record definition private and export an opaque type. This is not compatible with the current implementation as outside modules receiving the opaque type will not be able to use it with generated functions and meeting with approval from MR DIALYZER.

One idea is to allow a module to specify the type to use for the record. Or perhaps to simplify it, to specify that exporting the record type (as is now) or an opaque type for the record.