[docs] rlcompleter documentation

[Mark Ballard]

rlcompleter documentation doesn't show adequately how to switch it off.

This is important because rlcompleter is for some an unwelcome change
to the python interpreter.

It is unwelcome because it is poorly implemented.

It has disabled the tab key you would normally use to indent code in
the interpreter. It also appears to have broken the interpreter's
ability to accept cut-and-paste code on the command line
(http://www.gossamer-threads.com/lists/python/python/1086863). These
are both essential features for learners, for skething code and so on.

So I need to get rid of it.

But the Python documentation does not tell you how to switch it off:

https://docs.python.org/3/tutorial/interactive.html

(It has some surreal discussion that appears to refer to the missing
tab indent feature: 13.2. Alternatives to the Interactive Interpreter.
But sympathy is not much use here.)

That text includes a link from the words that say rlcompleter is
'automatically enabled'. This implies it will tell how to switch it
off as well.

It leads here:

https://docs.python.org/3/library/site.html#rlcompleter-config

(It is of course obvious that the rlcompleter is automatically
enabled. But I would challenge anyone who would  criticize this. The
Python documentation needs more statements of the obvious like, for
example, how to switch the rlcompleter off.)

The link goes to an arcane description of "site-specific" functions
that would be enough by now to deter most novices.

Persistence will get you to a description of the rlcompleter that says
you can turn it off by changing an attribute in your "sitecustomize or
usercustomize module or your PYTHONSTARTUP file".

So, determined now to find my Python startup file (that sounds like
something more substantial, more likely to be identified than these
customize modules), I follow the link to the given help page for
PYTHONSTARTUP:

https://docs.python.org/3/using/cmdline.html#envvar-PYTHONSTARTUP

That doesn't tell me where to find PYTHONSTARTUP. It even suggests I
might not have such a file at all!

I am by now so far from my original, simple problem that I'm beginning
to wish I'd taken a ball of string and unravelled it as I went so I
could find my way back again.

The Python interpreter help pages don't tell you how to switch
rlcompleter off either.

Looky here:

"
help> module rlcompleter
no Python documentation found for 'module rlcompleter'
"

It does suggest to me the documention is treated as an afterthought.
If whoever implemented this function was *answerable* to some sort of
appointed documentation representative then not only would the disable
function have been properly documented, but they might have been
forced to implement the disable feature properly because they would
have been forced to address awkward questions posed by someone with
such authority that they couldn't simply say, 'sod off documentation
worm, don't you know who I am - I've got far more important things to
do than bother with your pathetic, snivelling questions". Just a
thought.