Unicode support

I'm currently working with Matt Norton and Mike Howsden to improve and refine pycaption. It appears that pycaption doesn't handle string input in a fully correct manner as some of the conversion tests failed with no source editing after install. The tests that failed all were related to incorrect Unicode handling. 

After talking with Matt and Mike, they decided that pycaption should treat input strings as Unicode and only output Unicode (as opposed to the current setup which forces the input and output strings to be utf-8 encoded), and it should be the responsibility of the user to keep track of correct encodings. Therefore, I removed the byte string casts and updated the conversion tests to check the output caption string against the sample corresponding sample Unicode string.