Finish migrating C bindings to core bindings library

[Baltoli]

#897 begins the process of reorganising the functions in the C bindings into a new core bindings library that can be shared with Python; to keep the diff in that PR small only the features required to get term simplification working in Python were ported.

Once #897 is merged, we should finish the migration process and move the rest of the code from the C bindings over to the core library.