Beginning work on the new NeuroTools

NeuralEnsemble's NeuroTools repo started empty, so I've just started importing things in from the old NeuroTools trunk on the neuralensemble.org website.  I've kept the same file structure and names for now, although this can be reorganized, possibly be analysis type as Andrew has suggested.  I started with analog signals, and have:

1) Removed the NeuroTools AnalogSignal classes; everything now depends on Neo AnalogSignal classes.  
2) Most AnalogSignal class methods in NeuroTools related to analysis are now stand-alone functions.
3) Some AnalogSignal class methods recapitulate what Neo classes already support via Quantities, and have been removed.  
4) Methods related to plotting were moved to plotting.py as functions.  
5) The remaining AnalogSignal class methods have been moved into the Neo AnalogSignal classes, with implementation changes to work with Neo AnalogSignal classes, in particular Neo's AnalogSignalArray, which is quite different from NeuroTools's old AnalogSignalList.  
6) Forked python-neo, where I added the methods salvaged from (5).  I will make a pull request for that later.