Simplify `construct_stimulus` and document stimulus in `example-0.5-aln-external-stimulus`

[jajcayn]

A couple of things:

• delete construct_stimulus function from utils.stimulus; it has three modes and all of them can be achieved with ModelInput class:
  • ac is the same as SinusoidalInput
  • dc is the same as StepInput
  • rect can be easily done with a combination of ExponentialInput and StepInput with concatenation.. I will create RectifiedInput directly in the file
• create a shortcut for creating stimulus to core neurolib models... before it was something like construct_stimulus("ac", duration=model.params.duration, dt=model.params.dt, stim_amp=1.0, stim_freq=1); I propose SinusoidalInput(amplitude=1.0, period=1000.0).to_model(model), such that duration and dt of stimulation will be directly read from model.params
• revamp example-0.5-aln-external-stimulus:
  • swap all calls to construct_stimulus with new functions
  • create a section about ModelInput, what is implemented, how it looks like, what are the options (to_model, as_array, as_cubic_splines)
  • showcase SummedInput and ConcatenatedInput (need to wait for #162)

[caglorithm]

This is so nice. We should schedule a day on which we discuss the new stimulus class together.... When would be good for you?

[jajcayn]

today: anytime before 5pm; tomorrow: before interareal meeting; Wednesday: anytime

[caglorithm]

Wednesday noon @ 12?

[jajcayn]

works, adding to cal