Complete the online documentation of the models underlying the new electronic boards

[pattacini]

So far, we have just published the webview of the architectural model at https://robotology.github.io/icub-firmware-models.

[pattacini]

Alos, @valegagge raised the point that it may be somewhat beneficial to make available some documentation addressing the need for detailing the steps required to prepare, run and validate:

• the board per se
• the setup like the wrist mk2

[pattacini]

When we're happy with the model we've updated/modified, it's always a good rule to give a look at the codegen options and check if the C-mapping is ok.

Related to C-mapping, here's a quite enlightening resource. https://www.mathworks.com/help/rtw/ref/single-outputupdate-function.html.

Essentially, we can try to force the compiler to yield a single step function, but this choice may be overridden when we're dealing with multi-rate systems. As a result, the step function can be replaced by the pair update+output. The latter has something to do with the feed-through output signals.