Use gperf to save memory.

We check terms to see if they're in the wordlist, if they are we reuse
the string from the wordlist instead of allocating a new one.

(I've always wanted to use Gperf so I'm pretty stoked about this!)

implementations/C/Makefile

@@ -9,6 +9,8 @@ GPERF_OPTS = --readonly-tables --enum --includes --global-table
 
 joy: ${OBJS} $(STATIC_GCLIB)
 
-keywords.c: KEYWORDS.txt
+keywords.c: KEYWORDS.txt keywords.h
 	gperf --output-file=$@ --hash-function-name=keyword_hash $(GPERF_OPTS) KEYWORDS.txt
 
+# keywords.c doesn't strictly depend on keywords.h, but I want make to
+# remake if keywords.h is touched.