Doxygen: Display pico-sdk version number on all (doxygen) pages

[lurch]

At the moment the SDK version-number is visible on the "boxes page"

It might be nice if this was visible on every Doxygen page?

(but obviously only if @aallan agrees)

[aallan]

Yes, I think I agree with this one. The version number should be on all of the pico-sdk/* pages.