Problems with Sonderzeichen - like ö, ä and others

In TYPE_UTF8STR it would be helpful to have some utf-8 encoding and then work with the length of the encoded value. With this we are able to use other utf-8 encodes characters.

Please change so others can also use utf-8 characters.

```
if fieldid == EncoderConstants.TYPE_UTF8STR:
encoded_value = value.encode('utf-8')
content = encoded_value
length = len(encoded_value)
```