Make color emoji use character sequences instead of PUA.

The bitmap emoji tools are extended to create GSUB rules for character
sequences.  The images are renamed to code the character sequence in their
filenames.  New images are created for ASCII digits and number sign.  A new
script is added to add cmaps to the files for backward compatibility.

Makefile

@@ -20,6 +20,7 @@ EMOJI_PNG64 = ./png/64/emoji_u
 
 EMOJI_BUILDER = ../third_party/color_emoji/emoji_builder.py
 ADD_GLYPHS= ../third_party/color_emoji/add_glyphs.py
+PUA_ADDER = ../nototools/map_pua_emoji.py
 
 %.ttx: %.ttx.tmpl $(ADD_GLYPHS) $(UNI)
 	python $(ADD_GLYPHS) "$<" "$@" "$(EMOJI_PNG128)"
@@ -28,8 +29,10 @@ ADD_GLYPHS= ../third_party/color_emoji/add_glyphs.py
 	@rm -f "$@"
 	ttx "$<"
 
-$(EMOJI).ttf: $(EMOJI).tmpl.ttf $(EMOJI_BUILDER) $(EMOJI_PNG128)*.png $(EMOJI_PNG64)*.png
+$(EMOJI).ttf: $(EMOJI).tmpl.ttf $(EMOJI_BUILDER) $(PUA_ADDER) $(EMOJI_PNG128)*.png $(EMOJI_PNG64)*.png
 	python $(EMOJI_BUILDER) -V $< "$@" $(EMOJI_PNG128) $(EMOJI_PNG64)
+	python $(PUA_ADDER) "$@" "$@-with-pua"
+	mv "$@-with-pua" "$@"
 
 clean:
 	rm -f $(EMOJI).ttf $(EMOJI).tmpl.ttf $(EMOJI).tmpl.ttx