Make macros for header file names optional.

We no longer have to take care of the 8.3 file name limit; this
allows us (a) to introduce longer, meaningful file names, and (b) to
avoid macro names in `#include' lines altogether since some
compilers (most notably Visual C++) doesn't support this properly.

*/*: Replace

   #include FOO_H

with

   #include <freetype/foo.h>

or something similar.  Also update the documentation.
diff --git a/src/bdf/bdflib.c b/src/bdf/bdflib.c
index 63813f7..5c0fa40 100644
--- a/src/bdf/bdflib.c
+++ b/src/bdf/bdflib.c
@@ -33,10 +33,10 @@
 
 #include <ft2build.h>
 
-#include FT_FREETYPE_H
-#include FT_INTERNAL_DEBUG_H
-#include FT_INTERNAL_STREAM_H
-#include FT_INTERNAL_OBJECTS_H
+#include <freetype/freetype.h>
+#include <freetype/internal/ftdebug.h>
+#include <freetype/internal/ftstream.h>
+#include <freetype/internal/ftobjs.h>
 
 #include "bdf.h"
 #include "bdferror.h"