added integrator example
added a spike probe

call this with, e.g. model.probe('A.spikes')
then you have data=sim.data('A.spikes')
updated the many neurons notebook
standardizing notebooks and notebook naming
Updated spike probe with new connection types
Fixing typo in helpers.py
Add white noise signal generator

- Small connection change as well
Converted addition example to ipython
Converted multiplication example to ipython notebook
Addition example converted to ipython notebook
Multiplication example converted to ipython notebook
Squaring example converted to ipython notebook
Replaced all Transform,Filter,Decoder,Encoder with simple operations
Cleaning up comments
Added the skipped tests back in
attempting to add voltages probe
Fixed issue with neuron.voltage probe signal

- Wasn't being set with correct dimensions.
- Fixed __str__ function for simulator.ProdUpdate class.
- Updated comment regarding redefinition of signal dimensionality.
voltage probe working and demo'd

- Fixed incorrect asarray call
more careful error checking in SignalView.__init__
SignalView reshape for size==1