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, 1 insertions, 1 deletions

diff --git a/examples/howto-simple-svg.cxx b/examples/howto-simple-svg.cxx
index c3875e469..1b922f9f2 100644
--- a/examples/howto-simple-svg.cxx
+++ b/examples/howto-simple-svg.cxx
@@ -55,7 +55,7 @@ const char *svg_logo =
 int main(int argc, char **argv) {
 #ifndef FLTK_USE_SVG
     fl_message("You need to build FLTK with 'configure --enable-svg'\n"
-               "or CMake option 'OPTION_USE_SVG'\n"
+               "or CMake option 'FLTK_OPTION_SVG'\n"
                "to use this example.");
     return(1);
 #else