A big spring clean of the docstrings (sure long time coming!)
* Fix typos,
* rewrite clumsy explanations,
* omit unnecessary and misleading parts,
* remove awkward and "smart" language,
* use consistent here-doc formatting across small and big docstrings
(isolate quote mark triplets on own line.)
Not sure why but 2to3 suggested to enclose the % expression into
parentheses before passing it to print(); I did about the same thing
manually but a bit more readable.