Allow identifiers or scheme expressions evaluating to music after \with

Allow identifiers or scheme expressions evaluating to music after \with

This permits writing

   \with \voiceOne

instead of

   \with { \voiceOne }

which is mostly handy in the context of music/scheme function arguments.

[lemzwerg, 2013-09-10 10:28:06]

LGTM.

[janek, 2013-09-15 18:56:55]

As usual with my reviews: i definitely like the results, but i cannot say much
about the code.

thanks for another simplification!
Janek

[dak, 2013-09-15 19:16:55]

On 2013/09/15 18:56:55, janek wrote:
> As usual with my reviews: i definitely like the results, but i cannot say much
> about the code.
> 
> thanks for another simplification!
> Janek

It's not really a simplification: it's just moving one piece of code into
another lexer class.  If it were up to me, I'd probably throw out INITIAL mode
altogether, but when this was discussed previously, people felt that things like
.5\cm and 4.\cm were too important too give up (all of 0.5\cm, 4\cm and 4.0\cm
would continue to work) in layout/paper definitions.

At least at the current point of time, output definitions are the _only_ place
where the INITIAL lexer mode is still active.

[dak, 2013-09-15 19:18:44]

On 2013/09/15 19:16:55, dak wrote:
> On 2013/09/15 18:56:55, janek wrote:
> > As usual with my reviews: i definitely like the results, but i cannot say
much
> > about the code.
> > 
> > thanks for another simplification!
> > Janek
> 
> It's not really a simplification: it's just moving one piece of code into
> another lexer class.  If it were up to me, I'd probably throw out INITIAL mode
> altogether, but when this was discussed previously, people felt that things
like
> .5\cm and 4.\cm were too important too give up (all of 0.5\cm, 4\cm and 4.0\cm
> would continue to work) in layout/paper definitions.
> 
> At least at the current point of time, output definitions are the _only_ place
> where the INITIAL lexer mode is still active.

Oops, disregard this comment.  I thought we were talking about a different
issue.