documentation suggestion

[John Williams]

I think it would be extremely helpful for people attempting to tweak lilypond,
if there were examples in the documentation whenever a tweak is mentioned.  This
is already the case for most of the beginner's documentation, but when we get in
to the advanced documentation trying to write our own tweaks, the information
tends to be spread over many different pages, and requires several searches of
the mailings lists to find examples of the information actually put together
into a real tweak.

For example, section 4.5.1
<http://lilypond.org/doc/v2.11/Documentation/user/lilypond-learning/Moving-objects#Moving-objects>
talks about the extra-offset property, saying "It takes a pair of numbers..." 
It is quite rare to find a musician who also knows lisp well enough to translate
that phrase to "#'(1 . 2)".  But one example of an actual tweak in the
description would make that clear.

Other things examples could clarify is when context is required, or when one of
the tweak commands works better than others.  I like that lilypond tries to
determine the correct context when it is omitted, but if I see an example for
RehearsalMark (maybe on 3.1.80
<http://lilypond.org/doc/v2.11/Documentation/user/lilypond-internals/RehearsalMark#RehearsalMark>)
which says "\override Score.RehearsalMark #'extra-offset = #'(0 . 2)" then it
will help me realize that I should use override instead of set, and that the
Score context might be required in this situation.

I apologize for proposing a large project for which I am ill-equipped to help
out with, since I suck at tweaks and at texinfo.  But I think it would be the
biggest way to help me suck less at the former.  The above two examples could be
added to start with.

~ John Williams