Add: [Win32] Text layout using the native Windows Uniscribe library.

Uniscribe is sometimes producing different results compared to ICU, especially
when RTL and LTR content is mixed. Comparing the results to other programs
(like editors or web browsers) leads me to believe that the result are at least
not worse than ICU and possibly better.

src/fontcache.cpp

@@ -86,6 +86,7 @@ public:
 	virtual GlyphID MapCharToGlyph(WChar key) { assert(IsPrintable(key)); return SPRITE_GLYPH | key; }
 	virtual const void *GetFontTable(uint32 tag, size_t &length) { length = 0; return NULL; }
 	virtual const char *GetFontName() { return "sprite"; }
+	virtual bool IsBuiltInFont() { return true; }
 };
 
 /**
@@ -250,6 +251,7 @@ public:
 	virtual GlyphID MapCharToGlyph(WChar key);
 	virtual const void *GetFontTable(uint32 tag, size_t &length);
 	virtual const char *GetFontName() { return face->family_name; }
+	virtual bool IsBuiltInFont() { return false; }
 };
 
 FT_Library _library = NULL;