Fixes to macOS version to build on recent macOS versions and render correctly on high-DPI displays.

See merge request !6

Revert "Remove code branches using legacy KeyTranslate method. Should still work on MacOS >= 10.2 (released 2002)."

This reverts commit 432f6566.

Adjust text label size and line thickness to account for 2 pixels per 'point' in with high DPI displays.

Remove code branches using legacy KeyTranslate method. Should still work on MacOS >= 10.2 (released 2002).

gtk__cairo_should_draw_window() presence wasn't being tested.

Point to GitLab instead of Bugzilla (deprecated) in README

See merge request !4

Remove extern "C" warpper around atspi/glib headers inclusion

See merge request !3

Use Gtk 3's gtk_font_chooser_?et_font rather than Gtk 2's
gtk_font_button_?et_font_name

Recently glib headers started using C++ features when compled in C++
glib!1715 (commits)

This leads to errors like:
..
In file included from /usr/include/glib-2.0/glib/gatomic.h:31,
                 from /usr/include/glib-2.0/glib/gthread.h:32,
                 from /usr/include/glib-2.0/glib/gasyncqueue.h:32,
                 from /usr/include/glib-2.0/glib.h:32,
                 from /usr/include/at-spi-2.0/atspi/atspi.h:27,
                 from dasher_editor_external_atspi.cpp:5:
/usr/include/c++/11/type_traits:56:3: error: template with C linkage
   56 |   template<typename _Tp, _Tp __v>
      |   ^~~~~~~~
dasher_editor_external_atspi.cpp:4:1: note: 'extern "C"' linkage started here
    4 | extern "C" {
      | ^~~~~~~~~~
..

Since for a while now glib headers are supposed to be safe to include in
C++ code without extern "C" just remove it.