_get_res_string_value parsing error

[jtjisgod]

I parsed some string data from public xml and i tried bringing text value with _get_res_string_value("@string/text"). but it dosen't work! So, i found a mistake code from your core.py. "@string/" is 8, but you are slicing at 9. so, string_key is to be ext not text.

[cosmosgenius]

closed in #42. Thanks for the Issue and PR 👍