Add Examples: Peak Finding, Impedance

[bcliang]

new notebooks added to demo

[bcliang]

This is a bit of a follow-up to #16.

For our lab, we often are monitoring a well-characterized redox reaction at the electrode surface in which case the parser is used simply to extract the current readings at specific voltages. However, there are definitely cases where having peak detection is REALLY important (unknown reactions, drifting electrode potential, etc).

• Peak detection and area/integration are relatively common use cases in analyzing cyclic voltammetry curves. Should these be methods exposed within the subclass? I think there's a case for that, but I'm not yet convinced "data analysis" should be part of the code base.
• For the short term, I have written a simple demo python notebook which uses scipy.signal.find_peaks to identify peaks from a CV curve (thanks to code example from @p2jones). Perhaps in a future commit this type of functionality will be rolled in as a class method. Open to ideas/discussion on this topic.
• The second bit of issue CV add-ons: peak finding, plotting #16 is about visualization of curves. I personally prefer to keep display/plotting of data out of the parser code. Within our lab, some users prefer matplotlib while others opt for more interactive plotting libraries (e.g. plotly)

[p2jones]

Glad I could help a little. I agree that including plotting would really bloat the package.