pybricks.common.System.storage: use buffer protocol

This updates the storage method to allow any object with the buffer
protocol instead of just bytes.

Also change the missing arg error to a TypeError while we are touching
this.

Issue: #121

Author: dlech

pybricks/common/pb_type_system.c

@@ -115,21 +115,24 @@ STATIC mp_obj_t pb_type_System_storage(size_t n_args, const mp_obj_t *pos_args,
     mp_int_t offset = mp_obj_get_int(offset_in);
 
     // Handle read.
-    if (write_in == mp_const_none) {
+    if (read_in != mp_const_none) {
         byte *data;
         mp_uint_t size = mp_obj_get_int(read_in);
         pb_assert(pbsys_program_load_get_user_data(offset, &data, size));
         return mp_obj_new_bytes(data, size);
     }
 
     // Handle write.
-    if (read_in == mp_const_none && !mp_obj_is_str(write_in) && mp_obj_is_str_or_bytes(write_in)) {
-        mp_obj_str_t *obj = ((mp_obj_str_t *)MP_OBJ_TO_PTR(write_in));
-        pbsys_program_load_set_user_data(offset, obj->data, obj->len);
+    if (write_in != mp_const_none) {
+        mp_buffer_info_t bufinfo;
+        mp_get_buffer_raise(write_in, &bufinfo, MP_BUFFER_READ);
+
+        pb_assert(pbsys_program_load_set_user_data(offset, bufinfo.buf, bufinfo.len));
+
         return mp_const_none;
     }
 
-    mp_raise_ValueError(MP_ERROR_TEXT("Must set either read (int) or write (bytes)."));
+    mp_raise_TypeError(MP_ERROR_TEXT("Must set either read (int) or write (bytes)."));
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_KW(pb_type_System_storage_obj, 0, pb_type_System_storage);