Log Message:
cairomm1.16: update to 1.18.0.

1.18.0 (stable):

Meson build:
* The boost-shared option defaults to true
  (Kjell Ahlstedt)

1.17.1 (unstable):

* Add SaveGuard save/restore object
  (Jason Rhinelander, Kjell Ahlstedt) Issue #9 (Ian Britten)
* Add Surface::set/get_device_scale()
  (Thomas Holder) Merge request !22
* ScaledFont: Add get_text_extents() and get_glyph_extents()
  (Vitaly Dyachkov) Issue #30
* Use callback functions with C linkage
  (Kjell Ahlstedt) Issue glibmm#1 (Murray Cumming)

Documentation:
* Surface: Use cairomm names where possible
  (Kjell Ahlstedt)
* Context: Fix some typos
  (Daniel Boles) Merge request !26
* Update Visual Studio build docs
  (Chun-wei Fan) Merge request !28
* Remove AUTHORS and MAINTAINERS; add info to README.md
  (Kjell Ahlstedt) Issue gtkmm#140

Build:
* Meson build: Re-organize warnings-related compiler flags for MSVC
  (Chun-wei Fan) Merge request !24
* Autotools build: Add --disable-deprecated-api
  (Kjell Ahlstedt) Issue #29 (bbhtt)
* Require cairo >= 1.14.0
  (Kjell Ahlstedt)
* Meson build: Detect if we build from a git subtree
  (William Roy) Merge request gtkmm!72
* Meson build: Don't copy files with configure_file()
  (Kjell Ahlstedt)
* Meson build: Fix the evaluation of is_git_build on Windows
  (Kjell Ahlstedt) Issue gtkmm#131 (William Roy)