int sci_plugin_register(const BackendInfo *backend_info, RequestReturn *(*fill_meta_in)(const DocumentMeta *, size_t, size_t, void *), char *(*get_document_text_in)(const DocumentMeta *, void *), PdfData *(*get_document_pdf_data_in)(const DocumentMeta *, void *), void *user_data)
Registers a backend, not all functions have to be regisered for eatch backend, pass NULL for unwanted...