gbdb: refactor command parsing

Instead of passing around a string and having each command parse off
additional tokens, have a single command to parse all of the tokens,
and the commands can pass around a token list. Then each
command/subcommand can pop off whatever arguments they need.

Makefile

@@ -32,9 +32,11 @@ all: $(APPS)
 gbdb: apps/gbdb
 gbasm: apps/gbasm
 threading: apps/threading
+test-tokenize: apps/test-tokenize
+
 bmp: apps/bmp_test
 
-.PHONY: gbasm-test tests threading bmp
+.PHONY: gbasm-test tests threading bmp test-tokenize
 
 TESTS = $(patsubst %.o, %, $(filter %/test.o, $(ALL_OBJS)))
 tests: $(TESTS)