add a save_results method to DataReader class

[emmanuelfonseca]

we should add some functionality to have fitburst record or push fit results to user-specified places. for example, a general user will likely want things recorded to ASCII or .npz, whereas CHIME/FRB will want results reported to their database. my current thinking is to add a generic method to the DataReader base class, and then overload this in the fitburst/backend/chimefrb.py version of the DataReader to push things to FRBMaster.