FL_OVERRIDE is defined as `override` for C++11 and higher
FL_OVERRIDE is defined as `override` for VisualC 2015 and newer
Don't interfere with Fl_Widget::override()
Note that this fix includes "../src/flstring.h" which makes the source
file no longer compileable without the full source code, e.g. by
using "fltk-config --compile ...". This might be fixed later. (?)
Add coordinates and layout section to user manual
add section to user manual to clarify the use of window-relative
coordinates in both Fl_Group and Fl_Window containers, and include
brief descriptions of current layout manager widgets in one place.
add test/coordinates.cxx, test/wizard.cxx and related screenshots
under documentation/src.
update CMakeLists.txt, Makefile and .gitignore for new files.
Co-authored-by: Albrecht Schlosser <albrechts.fltk@online.de>
