move amalgamate tool to third_party folder

.gitignore

@@ -21,4 +21,3 @@ benchmarks/files/numbers/*.json
 cmake-build-debug
 
 test/test-*
-third_party/Amalgamate

Makefile

@@ -252,7 +252,7 @@ pretty:
 amalgamate: src/json.hpp
 
 src/json.hpp: $(SRCS)
-	develop/amalgamate/amalgamate.py -c develop/amalgamate/config.json -s develop --verbose=yes
+	third_party/amalgamate/amalgamate.py -c third_party/amalgamate/config.json -s develop --verbose=yes
 	$(MAKE) pretty