Function rsdb::c::rsdb_get

#[no_mangle]
pub unsafe extern "C" fn rsdb_get(
    db: *mut Tree, 
    key: *const c_char, 
    keylen: size_t, 
    vallen: *mut size_t
) -> *mut c_char

Get the value of a key. Caller is responsible for freeing the returned value with rsdb_free_buf if it's non-null.