This introduces a general way to use public enums both in the C++ and
the (upcoming) C API. For the C++ case, we now use enum classes rather
than enums for public enums. This also includes definitions for
C API to_string conversions for public enums. C API definitions in
cvc5_types.h are only included from the C API, guarded via a macro
(thus, for now, not included yet when the header is included).
The public cvc5 API now lives in the cvc5 namespace. All internal parts were moved into the (new) internal namespace.
The final hierarchy will be as follows:
cvc5
~~ public API
::context
::internal
::parser
::main
After this PR it will be:
cvc5
~~ public API
::internal
::context
::main
::parser
