* scm/output-lib.scm: Support of hammers and pulls in tablature

* scm/output-lib.scm: Support of hammers and pulls in tablature
-- Hammers and pulls are inserted exactly like slurs, and a "H" or
a "P" is added over the slur as needed.  The file

* ./input/test/tablature-hammer.ly: example of hammer, pull and
legato in a tablature.

* ly/engraver-init.ly: Stem.up-to-staff is now disabled by
default, since it appears that most of the published tablatures
are not like that.