title: unresolved external symbol "class Fl_Graphics_Driver * fl_graphics_driver"
body: <p>I am trying to implement a cpp project in Visual Studio 2017 on Windows 10 with FLTK and face the following error:  </p>
  
  <p>Severity    Code    Description Project File    Line    Suppression State
  Error   LNK2001 unresolved external symbol "class Fl_Graphics_Driver * fl_graphics_driver" (?fl_graphics_driver@@3PAVFl_Graphics_Driver@@A) Project 1   C:\Users\username\somefolder\Project1-Skeleton\ImageWidget.obj  1   </p>