Introduce "Modern CMake" in FLTK

This is a big commit and there are too many changes to list them all.
The main changes are:

- rename all CMake build options to 'FLTK_*'
- export library targets with namespace (prefix) 'fltk::'
- standardize shared library target names with suffix '-shared'
- set public build properties on libraries for consumers
- document library names and aliases in README.CMake.txt
- document changes in "Migrating Code from FLTK 1.3 to 1.4"
- partial backwards compatibility for old user projects

Included but not directly related changes:

- fix Windows (Visual Studio) DLL build
- add CMake function fl_debug_target() to show target properties
- don't build test programs if FLTK is a subproject
- internal: reformat CMake code: remove space before '('

Thanks to Matthias and Manolo for their help, testing, and feeback.

1 files changed, 3 insertions, 3 deletions

diff --git a/README.Wayland.txt b/README.Wayland.txt
index 7dd952690..f01147f5d 100644
--- a/README.Wayland.txt
+++ b/README.Wayland.txt
@@ -116,10 +116,10 @@ On Linux and FreeBSD systems equipped with the adequate software packages
 hybrid library. On systems lacking all or part of Wayland-required packages,
 the default building procedure produces a X11-based library.
 
-Use -DOPTION_USE_WAYLAND=OFF with CMake or "configure --disable-wayland" to build
-FLTK for the X11 library when the default would build for Wayland.
+Use "-D FLTK_OPTION_USE_WAYLAND=OFF" with CMake or "configure --disable-wayland"
+to build FLTK for the X11 library when the default would build for Wayland.
 
-CMake OPTION_WAYLAND_ONLY or "--disable-x11" configure argument can
+CMake option FLTK_BACKEND_X11=OFF or configure argument "--disable-x11" can
 be used to produce a Wayland-only library which can be useful, e.g., when
 cross-compiling for systems that lack X11 headers and libraries.