Split tutorial finger code into libraries

[hypatia]

I may change my mind about this one, but after editing the tutorial code last
night, and having to push my changes into three different files, I think it
might be better to have the application split into more than one file after a
certain point.

May well make it easier for readers to see what's being added at each point too,
as well as making the pages smaller again by *linking* to the already seen .py
files rather than including them in the HTML output, and only displaying .py
files containing new code at each step.

[kehander1]

finger19.tac libraries

[kehander1]

Something like this, then?

These are derived from the files in branch 25111. ( #532 )

[exarkun]

Good start. These files need to be actual Python source files though so that they can be imported from the rest of the listings, and the rest of the listings need to be updated to import them instead of re-defining what they contain. I also don't think it's a good idea to base these changes off of the #532 branch, unless you want to wait for #532 to be finished before doing any more work on this. If these changes are based on the #532 branch, then there's no way to apply them until #532 is resolved. Doing this refactoring first based on trunk might also make #532 easier to resolve.