feat(ffi): define external functions for get a default logger and for set a...

Summary

• feat(ffi): define external functions current_cord_name, cord_is_main and cord_is_main_dont_create.
• feat(ffi): define external functions for get a default logger and for set a logging format function.

Ensure that

• New code is covered by tests
• API is documented
• Changelog is up to date
• Version is bumped in the appropriate Cargo.toml files