stub out linux demon; linux font provider; begin work, get windows/events up and running in os_gfx

src/font_provider/font_provider_inc.h

@@ -8,12 +8,17 @@
 //~ rjf: Backend Constants
 
 #define FP_BACKEND_DWRITE 1
+#define FP_BACKEND_FREETYPE 2
 
 ////////////////////////////////
 //~ rjf: Decide On Backend
 
-#if !defined(FP_BACKEND) && OS_WINDOWS
-# define FP_BACKEND FP_BACKEND_DWRITE
+#if !defined(FP_BACKEND)
+# if OS_WINDOWS
+#  define FP_BACKEND FP_BACKEND_DWRITE
+# elif OS_LINUX
+#  define FP_BACKEND FP_BACKEND_FREETYPE
+# endif
 #endif
 
 ////////////////////////////////
@@ -26,6 +31,8 @@
 
 #if FP_BACKEND == FP_BACKEND_DWRITE
 # include "dwrite/font_provider_dwrite.h"
+#elif FP_BACKEND == FP_BACKEND_FREETYPE
+# include "freetype/font_provider_freetype.h"
 #else
 # error Font provider backend not specified.
 #endif