Adds a glyph for tied lyrics. (issue4808074)

[bordage . bertrand]

Reviewers: ,

Message:
Better handling of lyric ties:
* The space between two tied words is no more fixed. Its value is
word-space. The default space is therefore decreased.
* New glyph, so that we won't need an external font.
* Increased vertical space between words and tie. It is therefore now
possible to have commas in tied lyrics without any collision (example:
verte,~et).

How to build it:
rm mf/out/feta*
make

Regards,
Bertrand

Description:
Adds a glyph for tied lyrics.

Please review this at http://codereview.appspot.com/4808074/

Affected files:
  M Documentation/de/notation/vocal.itely
  M Documentation/es/notation/vocal.itely
  M Documentation/fr/notation/vocal.itely
  M Documentation/notation/vocal.itely
  M mf/feta-generic.mf
  M mf/feta-test-generic.mf
  A mf/feta-ties.mf
  M scm/define-markup-commands.scm