Function indy_sys::anoncreds::indy_prover_fetch_credentials_for_proof_req

#[no_mangle]
pub unsafe extern "C" fn indy_prover_fetch_credentials_for_proof_req(
    command_handle: CommandHandle, 
    search_handle: SearchHandle, 
    item_referent: CString, 
    count: usize, 
    cb: Option<ResponseStringCB>
) -> Error