Port obsolete C stub functions to Rust
Three obsolete functions in the C API are still implemented in C. They just g_return_if_blah()
and return NULL immediately.
rsvg_handle_get_metadata
rsvg_handle_get_title
rsvg_handle_get_desc
We should move these functions to c_api.rs as part of moving the whole library to Rust.
Edited by Federico Mena Quintero