basic py3.3 compatibility while keeping py2.7 compatibility

makes the api callable from py2.x and py3.x. Since scrapy itself is not yet python3 compatible this might be still useful if one has a control application/api written in py3 which should be able to control scrapy crawlers. 
i've just checked the documentation. In py3 it defaults to utf-8 but in py2 it defaults to system default. So yes, its better to declare the encoding explicit.