Add tab-tie-follow-engraver (issue2723043)

[Carl . D . Sorensen]

Reviewers: carl.d.sorensen_gmail.com,

Message:
Here's a patch to Marc's tab stuff that has the engraver moved to a C++
engraver instead of a Scheme engraver.  This should help get it into the
source tree before 2.14.

Thanks,

Carl


Description:
Add tab-tie-follow-engraver
Based on the Scheme engraver in Marc Hohl's pack

Please review this at http://codereview.appspot.com/2723043/

Affected files:
  A lily/tab-tie-follow-engraver.cc
  M ly/engraver-init.ly
  M ly/property-init.ly
  M scm/define-grob-interfaces.scm
  M scm/define-grob-properties.scm
  M scm/tablature.scm