0.9.0

This is a relatively small release fixing problems found in the initial lessons of using the drudge script. Specifically, bugs with pickling symbols in drudge scripts has been fixed. Also, generally better error handling and reporting can be seen in using drudge scripts. To facilitate advanced manipulation inside drudge scripts, tensors are also given a full pack of three core manipulation functions, map, filter, and bind. Also, the documentation has been improved.