Adjust handbook to refer to "processor" not "sonde"

[ninarobbins]

The sonde module is now called processor, and the example notebooks don't work with "sonde"

[Geet-George]

Ah, yes. This change could also make it into PR #112.

[hgloeckner]

I marked them in PR #138 as outdated. I think that there are more functions missing now, but did not have the time to check thoroughly