Tidy up and split appendix A

[MichaelClerx]

It's a mess. Can never find anything.

Let go of cited order

Topics:

• op amps - ideal & non-ideal
• laplace
• filters
• filters, digital emulators
• bessel filters - laplace
• bessel filters - ode
• stimulus filter
• heka filters, generally?

Something like that, with an order not determined by the big 4

[MichaelClerx]

Example of hard to find things:

• Time constant for 1-pole filter as function of cut-off frequency
• Time constant for 1st order stimulus filter