Do not include farsi.c in main.c

- Change CMakeLists.txt to compile farsi.c normally
 - Add const to global variables in farsi.h and define them in farsi.c (no need
   to include farsi.h with DO_INIT defined in globals.h)
 - Include farsi.h where necessary
 - Include all necessary headers in farsi.c
 - Move farsi function declarations from main.h to farsi.h

src/normal.c

@@ -24,6 +24,7 @@
 #include "ex_cmds2.h"
 #include "ex_docmd.h"
 #include "ex_getln.h"
+#include "farsi.h"
 #include "fileio.h"
 #include "fold.h"
 #include "getchar.h"