Create skylines directly from glyph outlines. (issue 561730043 by address@hidden)

[hanwenn]

Reviewers: ,

Message:
goes on top of https://codereview.appspot.com/581960043/

Description:
Create skylines directly from glyph outlines.

This avoids creating garbage for the intermediate Scheme data to
transport the glyph outlines.

Benchmark:

benchmark for arguments: input/regression/mozart-hrn-3.ly
raw data: {'ac8eaa37ee': [2.73, 2.7, 2.73], '893552a691': [2.7, 2.71,
2.71]}
  med diff -0.732601 % (893552a691 is faster)

benchmark for arguments: -I carver MSDM
raw data: {'ac8eaa37ee': [52.43, 52.41, 52.17], '893552a691': [52.47,
52.33, 52.18]}
893552a691 - Create skylines directly from glyph outlines.
  med diff -0.152643 % (893552a691 is faster)

(for Carver score, the difference is at noise)

Please review this at https://codereview.appspot.com/561730043/

Affected files (+50, -90 lines):
  M lily/freetype.cc
  M lily/include/freetype.hh
  M lily/include/lily-proto.hh
  M lily/include/open-type-font.hh
  M lily/include/pango-font.hh
  M lily/open-type-font.cc
  M lily/pango-font.cc
  M lily/stencil-integral.cc