[buffer] Implement buffer deserialization for format=text

Using a ragel machine.

src/Makefile.am

diff --git a/src/Makefile.am b/src/Makefile.am
index a908c49..f666d5e 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -258,11 +258,13 @@
 .PHONY: unicode-tables arabic-table indic-table
 
 BUILT_SOURCES += \
+	hb-buffer-deserialize-text.hh \
 	hb-ot-shape-complex-indic-machine.hh \
 	hb-ot-shape-complex-myanmar-machine.hh \
 	hb-ot-shape-complex-sea-machine.hh \
 	$(NULL)
 EXTRA_DIST += \
+	hb-buffer-deserialize-text.rl \
 	hb-ot-shape-complex-indic-machine.rl \
 	hb-ot-shape-complex-myanmar-machine.rl \
 	hb-ot-shape-complex-sea-machine.rl \