[docs] master list of file properties

[John Hensby]

The TextIOWrapper has a name attribute,
but that fact not easily discovered because
name is mentioned only under 15.2.3. *Raw* File I/O.

Would it be a good idea to make a list of all the
properties that are possessed by most normal files,
and put it where the user-in-a-hurry can find it easily.
Linking to it from the builtin open function may help too.

Sorry I don't have time to do it myself.

-- jh