adds documentation for the new bar line interface (issue 6742061)

[pkx166h]

Thanks for doing this.

Some comments (it's the one thing I feel competent enough to join in and
make suggestions on).

James


https://codereview.appspot.com/6742061/diff/2001/Documentation/notation/rhythms.itely
File Documentation/notation/rhythms.itely (right):

https://codereview.appspot.com/6742061/diff/2001/Documentation/notation/rhythms.itely#newcode2765
Documentation/notation/rhythms.itely:2765: New bar line styles can be
defined with @code{\defineBarLine}.
Could we have some

@funindex \defineBarLine
@cindex bar lines, defining
@cindex defining bar lines

or some similar case - I haven't checked this in the current documents
to see what else we are using.

https://codereview.appspot.com/6742061/diff/2001/Documentation/notation/rhythms.itely#newcode2779
Documentation/notation/rhythms.itely:2779: The second argument is a list
containing three entries
I think you need to clarify this more. I cannot see what the 'second
argument' is.

So for example if you look here:

http://lilypond.org/doc/v2.16/Documentation/notation/the-set-command

you can see that we list the command with appropriate @var{..}. That
would help the non-technical user to at least get a handle on the
command in full.

Then move this para above the @lilypond (after the \defineBarLine @var{}
@var{}

and this is more coherent to read.

https://codereview.appspot.com/6742061/diff/2001/Documentation/notation/rhythms.itely#newcode2781
Documentation/notation/rhythms.itely:2781: beginning of the next line
and as a span bar, respectively.
Is there any merit in @ref{}ing
http://lilypond.org/doc/v2.16/Documentation/notation/visibility-of-objects#using-break_002dvisibility

Or perhaps giving an equivalence?

https://codereview.appspot.com/6742061/diff/2001/Documentation/notation/rhythms.itely#newcode2783
Documentation/notation/rhythms.itely:2783: There are currently eleven
glyphs available:
See my comment below about the term 'glyphs'.

https://codereview.appspot.com/6742061/diff/2001/Documentation/notation/rhythms.itely#newcode2789
Documentation/notation/rhythms.itely:2789: segno sign, and @code{"["}
and @code{"]"} for the brackets.
Would it be too much to have an @lilypond example for all of them?
Instead of just listing them

https://codereview.appspot.com/6742061/diff/2001/Documentation/notation/rhythms.itely#newcode2796
Documentation/notation/rhythms.itely:2796: The @code{"-"} sign allows to
distinguish bar lines with
The @code{"-"} sign distinguishes bar lines that have identical...

https://codereview.appspot.com/6742061/diff/2001/Documentation/notation/rhythms.itely#newcode2802
Documentation/notation/rhythms.itely:2802: way to define new bar line
glyphs.  For more informations
are these actually 'glyphs'? I ask because if they are then they need to
appear somewhere like here:

http://lilypond.org/doc/v2.16/Documentation/notation/the-feta-font

I've never really understood why bar lines (apart from the very fancy
scripts.varsegno) are not listed here. I am guessing they are not glyphs
and this therefore needs to be corrected?

https://codereview.appspot.com/6742061/